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Tuning 3 x 45 DCOE 3 Webers


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#176 natcamp10

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Posted 13 June 2018 - 08:33 PM

I got the Stubbs today and Kieth said that he has not modified the tubes but said run all
6 holes and if it runs a little lean to ream the hole as out , james what size holes should they be if this is required ?
Nathan

#177 jd lj

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Posted 14 June 2018 - 05:33 AM

When using the O6 tubes with the std 1mm bubbling holes the size of the air correctors relates to the number of bubbling holes left open.

The formula is: the air correctors cross sectional area must be 1/3 of all the open bubbling holes cross sectional area when added together. This gives you the cross sectional area of the hole in the air correctors and not the diameter, that must be then worked out based on the area. Luckily I've listed the sizes here for you. This way you are using the smallest air corrector possible to do the job this will minimise the mixture leaning out as rpm's rise.

-2 holes open = 85 air correctors
-3 holes open = 100 air correctors
-4 holes open = 115 air correctors
-5 holes open = 130 air correctors
-6 holes open = 145 air correctors

To plug any holes not needed during testing just use the tip of a tooth pick, shoved it in the hole and snap it off. These can easily be removed later if required and works very well. I've driven over a 600 km round trip with tooth picks in the emulsion tubes without any issues. Just a bit of tooth pick tuning. Once you've established the required number of holes the others can be plugged with high strength loctite and heating it up until it looses it's shine and goes hard, don't over heat it and burn it though.

By altering the number and or size of the bubbling holes you'll change the mixture strength when the main circuit tips in. So for the learning experience try it with two holes and then with six holes open. I just solder up the holes in the air correctors and drill them out to suit.

James D

#178 jd lj

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Posted 14 June 2018 - 05:39 AM

I found that six 1mm bubbling holes open was good but still needed a little bit more mixture strength at tip in. Five holes at 1.25mm with a 160 air corrector was very good.

When I tried six holes at 1.25mm with the matching 175 air correctors I was actually getting a new hesitation at tip in because it got rich enough to momentarily flood the engine.

James D

#179 jd lj

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Posted 17 June 2018 - 09:01 AM

Tip for the day,
I'm currently working on a set of triple 45dcoe152's which two out of the three carbs have there barrels flowing very differently from each other when tested with the air flow synchronising tool. When these were set up on the engine we'd had to use the air bypass screws to balance out the difference, if these had been on one of the earlier model dcoe's without the air bypass screws then balancing them wouldn't have been possible.
So whilst the carbs are off with his new motor going in I've bolted each carb to a box that I've made up to which I attach my workshop vacuum to the other end and then use my synchronising tool to sync each carb prior to fitting them to an engine or in this case synchronising the barrels to match each other. This box has a clear perspex lid and a rubber seal so that I can test various jetting modifications and visually compare the difference.

If the throttle plates are adjusted correctly and the two barrels still flow different amounts of air then there's a good chance that the spindles are slightly twisted, especially on used carbs. I believe that this is caused by people tightening up the nuts on the ends of the spindles without supporting the spindle adequately. My recommendation is to tighten the spindle nuts just enough to be firm and use a piece of approximately 2mm thick by approximately 20mm wide aluminium folded to a "U" shape to slide over the throttle plate and the spindle hard up against the edge of the barrel closest to the nut that you are tightening and holding this with a pair of pliers etc. This technique is shown in Des Hammils book on dcoe's. This should reduce the twisting force being applied to the spindles. Excessive force isn't required on the spindle nuts to keep them on as they have locking tabs anyway. Alternatively a locknut could be used, the spindles have a M7 thread from memory.

If for some reason you have to change the lever arm on the spindle then the carb should be taken off the manifold so that the spindle can be supported as described above whilst loosening and re-tightening the spindle nuts.

These carbs that I'm working on should no longer need the use of the air bypass screws to balance each barrel of each carb. When the air bypass screws are needed for this purpose then if the chokes need to be changed then these screws need to be removed and readjusted once it's all reassembled.

The air bypass screws can also be tweaked to help adjust the idle to get the throttle plates to be positioned directly below the first progression hole at idle in some cases.

James D

#180 natcamp10

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Posted 18 June 2018 - 09:51 PM

Tip for the day,
I'm currently working on a set of triple 45dcoe152's which two out of the three carbs have there barrels flowing very differently from each other when tested with the air flow synchronising tool. When these were set up on the engine we'd had to use the air bypass screws to balance out the difference, if these had been on one of the earlier model dcoe's without the air bypass screws then balancing them wouldn't have been possible.
So whilst the carbs are off with his new motor going in I've bolted each carb to a box that I've made up to which I attach my workshop vacuum to the other end and then use my synchronising tool to sync each carb prior to fitting them to an engine or in this case synchronising the barrels to match each other. This box has a clear perspex lid and a rubber seal so that I can test various jetting modifications and visually compare the difference.

If the throttle plates are adjusted correctly and the two barrels still flow different amounts of air then there's a good chance that the spindles are slightly twisted, especially on used carbs. I believe that this is caused by people tightening up the nuts on the ends of the spindles without supporting the spindle adequately. My recommendation is to tighten the spindle nuts just enough to be firm and use a piece of approximately 2mm thick by approximately 20mm wide aluminium folded to a "U" shape to slide over the throttle plate and the spindle hard up against the edge of the barrel closest to the nut that you are tightening and holding this with a pair of pliers etc. This technique is shown in Des Hammils book on dcoe's. This should reduce the twisting force being applied to the spindles. Excessive force isn't required on the spindle nuts to keep them on as they have locking tabs anyway. Alternatively a locknut could be used, the spindles have a M7 thread from memory.

If for some reason you have to change the lever arm on the spindle then the carb should be taken off the manifold so that the spindle can be supported as described above whilst loosening and re-tightening the spindle nuts.

These carbs that I'm working on should no longer need the use of the air bypass screws to balance each barrel of each carb. When the air bypass screws are needed for this purpose then if the chokes need to be changed then these screws need to be removed and readjusted once it's all reassembled.

The air bypass screws can also be tweaked to help adjust the idle to get the throttle plates to be positioned directly below the first progression hole at idle in some cases.

James D


That is a very good tip James

#181 natcamp10

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Posted 18 June 2018 - 10:09 PM

James if you were to go about a throttle plate adjust or check proceedure on a set of 152 that were bolted to a engine , I’ve read many things but basically I’ve balanced mine a few times but I’m not 100 percent sure they are all synchronised perfectly .
So here is how I’ve ben doing it with a synchronising meter . I back off the ofleadjustment screw till it does nothing , I then take the adjustment screws down till they touch the add about 1/8 to 1/4 turn , i the. Put my meter on it a and check what eAch carb is doing , I do find there a little out so I then go to the linkage adjustment to balance but thinking about it I would be changing the buttery adjustment by doing this , so how would you go about do this on carbs that are mount on a engine ?

#182 jd lj

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Posted 20 June 2018 - 06:42 PM

With the engine warmed up to operating temperature use the synchronising meter to check the flow on each carb, use the same barrels of each carb each time you check it. Hopefully both barrels of each carb are flowing the same amount and if not then adjust the air bypass screws (on the later model dcoe's). If you need to adjust any carb loosen the top lever arm on the linkage rod and then adjust the throttle stop screw on the carb or carbs that need adjusting to achieve equal flow rates on all three carbs. Then if the idle rpm's are not where you like them (my engine is happy idling at 1000rpm's) then adjust all three throttle stop screws by the same amount until the engine is idling happily. Recheck the synchronisation off all three carbs if you had to change the idle rpm's. If you're happy with it re-tighten the top lever arms onto the linkage rod but when doing so make sure that you are holding the carb spindle lever hard up to the throttle stop screws and I also use another finger on the same hand to pull the top lever down whilst tightening the locking bolt to eliminate any slack in the linkages, I hope that makes sense. Once everything is tight go back and check the flow rates are all the same in case you bumped anything whilst tightening it all up.

Some books will say that you should always bring the highest flowing carb down to the others, but I don't necessarily agree with that because sooner or later you need to get the rpm's to where the engine is happy to idle. So I think that you can adjust them either up or down if you want as long as they're all flowing the same in the end and the idle rpm's are suitable.

My synchronising tool usually reads around the number 6 at idle, so that my guide you towards whether you need to adjust the throttle stops up or down depending on what your readings are when you start. If it's reading 5 wind the throttle stop screw in or if it's 7 or so wind the throttle stop screw out. 6 is just my baseline setting and you may want it higher or lower to suit you and your engine.

You should also check the synchronisation at around 2000-3000 rpm's.

Linkages with the hex rods can be a pain to synchronise properly sometimes, you may have to make compromises.

If the manifold is poorly designed and the carbs aren't all on the same plane then it's unlikely that you'll be able to synchronise everything both at idle and throughout the rev range.

James D

#183 LC-GTR-1969

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Posted 24 June 2018 - 02:04 PM



You should also check the synchronisation at around 2000-3000 rpm's.

Linkages with the hex rods can be a pain to synchronise properly sometimes, you may have to make compromises.

 

 

I agree JD regarding these two comments... Many only sync at idle but in my experience, sync at idle and quite often you can be out when holding 3000rpm... I actually prefer to have perfect sync at 2000, 3000 then 4000rpm as opposed to being finicky about idle, but thats just me..

 

Also the hex rods are painful. I bought my billet linkages and drop links and never looked back... best $300 spent. Seams like a lot- but the hex bar was just so painful and I also noticed that the redline hex bar had a fair bit or twist along it when applying revs, so no matter what I did I would always have the front car slightly trailing the rear two. Just woeful. Dont get me wrong, I made them work for about 3 years but then cracked it and just put a good set on. 



#184 natcamp10

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Posted 24 June 2018 - 10:21 PM

Im on it gents . Got all week to play around with the carbs in the shed and also got my 06 tubes in the mail today so there going in as well
Also so found a good blue motor crank to go into my engine build that I’m starting
Nath👍

#185 jd lj

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Posted 25 June 2018 - 05:16 AM

Have fun Nathan. Keep us updated and I'll advise you what to do next where possible.

#186 natcamp10

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Posted 02 July 2018 - 09:51 PM

Ok turns out I wasn’t far out with the synch between the carbs , haven’t had anytime to data log but had a couple of drives with the o6 tubes with all holes in use , a lot smother through the rev range
I have a odd ball question as I’m chasing a 45mm Italian dcoe 152 body assembly . I have found a 45mm dcoe 150 series carb and from what I’ve found out is that everything will swap over and it will turn it into a 152 carb as the transition ports are the same between a 150 and a 152 model Italian carb .Jd or anyone are you able to confirm this?
Cheers
Nathan 👍

#187 jd lj

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Posted 03 July 2018 - 05:33 PM

Hi Nathan,
All the parts are interchangeable between the dcoe models as long as the size is the same except for the early model have a M8 thread for the progression holes covers and the later ones such as the 150's & 152's use a M9 thread for the cover.

I think that I have photos of the progression holes on both those models but only have sizes of the holes for the 152's. A 152 will show up soon enough.

What part of yours is cracked, the mounting flange or one of the barrels where the choke or AV locking screw go? If it's the flange it's probably not really repairable the locking screws section can be welded.

I'm glad that the O6 tubes are working well for you.

James D

#188 jd lj

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Posted 03 July 2018 - 06:57 PM

Ok turns out I wasn’t far out with the synch between the carbs , haven’t had anytime to data log but had a couple of drives with the o6 tubes with all holes in use , a lot smother through the rev range
I have a odd ball question as I’m chasing a 45mm Italian dcoe 152 body assembly . I have found a 45mm dcoe 150 series carb and from what I’ve found out is that everything will swap over and it will turn it into a 152 carb as the transition ports are the same between a 150 and a 152 model Italian carb .Jd or anyone are you able to confirm this?
Cheers
Nathan


Looking through my collection of progression hole patterns the 150 and the 152 the progression hole pattern's do look very similar, but I'm unsure if the diameters and positioning are the same.

I've sent you a pm about a 152 that's available.

James D

#189 jd lj

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Posted 28 July 2018 - 06:02 PM

The following statement came up on Sidedraft Central recently and I thought that it's a good brief description of why these VF tubes out perform std weber emulsion tubes.

The problem with the bubbling e-tubes is the sheer quantity bubbles to required to elevate the fuel that high means that at WOT those bubbles are leaning out the mixture as the rpms climb. If you get rid of the bubbles, that problem goes away. These VF tubes are simply air driven fuel injectors and will not behave in that manner.
-Keith Franck
http://Webstore.com/~DCOE_Tuner

James D

#190 jd lj

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Posted 26 August 2018 - 08:54 AM

From time to time there's mention of David Vizard's theory on emulsion tube selection, I think that it was even brought up earlier in this thread. His suggestion is along the lines of, take an emulsion tube and turn it upside down and look at where the holes are. Doing this will tell you if that type of tube is rich or lean at a particular rev range whereby if the holes are at the bottom of the upside-down tube then the bottom end of the main circuit will be lean and vice versa. However what David fails to point out is the relationship of the holes in regards to the fuel level and how important it is to have the fuel level set at the correct height. If those holes are above the fuel level (when the tube is in the carb) they will lean out the mixture, but if those same holes were below the fuel level they would now richen up the mixture. The difference could be as simple as a change in the fuel level by as little as 1-2mm.

If you set the fuel level to 25mm down as I described earlier in this thread and used some of the tubes that I've recommended then this situation can be avoided along with all the associated problems of hesitations on the transition from the progression circuit to the main circuit.

The VF tubes are also available for DHLA dellorto's along with other types of webers.

James D

#191 jd lj

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Posted 26 August 2018 - 09:20 AM

It should be pointed out that achieving a fuel mixture control comparable to fuel injection isn't going to happen with a carburettor with only a few circuits. Webers require a richer fuel mixture than fuel injection to provide excellent tractability. This is essentially what killed off the use of carburettors on production cars once catalytic converters became mandatory. The catalytic converters require a leaner mixture than what a smooth running dcoe will provide to supply the converter with enough oxygen for the chemical reaction to take place.

Due to this anyone using dcoe's will have to accept that having a 14.7 AFR cruising mixture and still retaining good tractability and then a 12.5 AFR mixture at WOT to achieve maximum power simply isn't going to happen. Your low power cruise mixture is going to require a richer mixture than up around 14+ AFR otherwise stumbles/ hesitations will be the result.

With that being said although dcoe's won't operate well with a mixture spread comparable to fuel injection it is possible to achieve a smoothness in tractability comparable to fuel injection with no hesitations, stumbles, surges or roughness what so ever.
It just requires an understanding of the inner workings of the dcoe's, some diagnostic equipment, time and patience and a well designed set up. Skimping on the quality of linkages etc comes at a high price.
Don't expect to tune your dcoe's to such a high level in one afternoon though.

James D

#192 Brian Pascoe

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Posted 29 August 2018 - 11:30 AM

Hi James,

I finally have another diff. 3.08:1.Just wondering what you recommend for my setup.I will be be rebuilding it in the next week or so and then its back to tuning the old girl.

Brian



#193 LC-GTR-1969

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Posted 29 August 2018 - 01:33 PM

Hi James,

I finally have another diff. 3.08:1.Just wondering what you recommend for my setup.I will be be rebuilding it in the next week or so and then its back to tuning the old girl.

Brian

 

Are you seeking advice on the diff? If yes, what tyre size are you running? ie 225/50r15 etc.. Also, what gearbox/trans and what ratios? 3.08 single spinner is not ideal in anything even mildly modified- but in order to give sound diff advice, the tyre size and gearbox/ trans / torque converter stall size etc need to be taken into consideration. Also, what cam specs? A long duration cam wants a shorter diff gear to pull it off the line. Stockish cams can generally pull taller diff gears. 



#194 jd lj

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Posted 16 September 2018 - 03:37 PM

Hi Brian,
I hadn't replied earlier to your above post because LC-GTR-1969 had already summed it all up so well.

James D

#195 jd lj

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Posted 16 September 2018 - 03:57 PM

Fuel pressure regulators

I got a call recently to replace the spindle return spring inside a dcoe that had snapped and the car was also not running right.

Once the spring was changed and the carb refitted I proceeded to resynchronise the carbs. I'd set the idle and all seemed ok momentarily but when we'd give it a rev the rpm's wouldn't return to where I had set them, it'll be idling much higher but would then gradually drop until it stalled. No jetting had been changed or idle mixture screws touched but the plugs were black.

The problem turned out to have been that the owner had fitted a new fuel pump and wasn't running a fuel pressure regulator. Having no reg hadn't presented any problems with the old fuel pump but the new pump was obviously putting out more psi which was then pushing past the needle and seats and flooding the engine. Both pumps were just the std mechanical fuel pumps off early commodore's but obviously the new pump had a less fatigued spring which created more psi. Another problem that I had noticed whilst synchronising the carbs was that there was an few drops of fuel coming out of the ram tubes onto the inner guard at idle which had never happened with this engine before.
Upon fitting a pressure regulator and setting it to 2.5-3 psi, and cleaning the plugs again then everything ran perfectly again and the drops of fuel coming out of the ram tubes also stopped.

So make sure that you are using a fuel pressure regulator with your dcoe's.

James D

#196 LC-GTR-1969

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Posted 17 September 2018 - 12:14 PM

Fuel pressure regulators

I got a call recently to replace the spindle return spring inside a dcoe that had snapped and the car was also not running right.

Once the spring was changed and the carb refitted I proceeded to resynchronise the carbs. I'd set the idle and all seemed ok momentarily but when we'd give it a rev the rpm's wouldn't return to where I had set them, it'll be idling much higher but would then gradually drop until it stalled. No jetting had been changed or idle mixture screws touched but the plugs were black.

The problem turned out to have been that the owner had fitted a new fuel pump and wasn't running a fuel pressure regulator. Having no reg hadn't presented any problems with the old fuel pump but the new pump was obviously putting out more psi which was then pushing past the needle and seats and flooding the engine. Both pumps were just the std mechanical fuel pumps off early commodore's but obviously the new pump had a less fatigued spring which created more psi. Another problem that I had noticed whilst synchronising the carbs was that there was an few drops of fuel coming out of the ram tubes onto the inner guard at idle which had never happened with this engine before.
Upon fitting a pressure regulator and setting it to 2.5-3 psi, and cleaning the plugs again then everything ran perfectly again and the drops of fuel coming out of the ram tubes also stopped.

So make sure that you are using a fuel pressure regulator with your dcoe's.

James D

 

I can second this. 

 

I was helping fix some spark plug fouling issues with twin IDF webers on a VW beetle (2.4l stroker engine), and the fouling issue was mainly to do with the fact that no regulator was run.

 

The owner was explicitly told by his mechanic that he did not need one- but in my honest opinion, WEBERS and SUs should all have fuel pressure regs. You can get away with it with some pumps but honestly dont bother trying, just in stall a regulator and be done with it. I run 2.5PSI with webers and about 3PSI with SUs. 

 

Since we installed the fuel pressure reg- the issue seems fixed. Electric fuel pumps can build a fair bit of pressure. In honesty, with any carb with an electric fuel pump, I would be running a regulator. Not a lot of expense really, and easy to set up. 






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