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TR6 TR6 Weber Carb Conversion

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DanNagy

DanNagy

Jedi Trainee
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<span style="text-decoration: underline">Car</span>: 1974 TR6

<span style="text-decoration: underline">Problem</span>: Weber Dual DGV downdraft carb conversion completed on rebuilt engine, car is backfiring through carbs and stalls at stop. It also seems to be burning rich as the fumes waft back to me while driving. Adjustments to the carbs don't seem to help. My TR6 experience is limited, but I can't believe it normally runs so rich as to smell raw gas.

<span style="text-decoration: underline">Research</span>: I did a search of the site but could not find an answer. I also searched the www and couldn't find the exact answer.

<span style="text-decoration: underline">History</span>: I have been in here before whining about this, and thought I would redo the distributor and hot things up. I didn't do that because I wanted to understand what was going on for a change. After reading all I could, my vague understanding is that the problem is with the carbs, so I didn't want to add changing the distributor into the mix of problems. I tried adjusting the Webers, and so has my mechanic.

<span style="text-decoration: underline">Advice received</span>: My mechanic, who I think is a mechanical genius, tells me I haven't run the car enough since its restoration and breaking it in may solve the problem. Maybe he thinks that after the engine has a few more thousand miles on it, the the carbs will work better.

<span style="text-decoration: underline">My opinion</span>: Okay, I am a complete idiot when it comes to mechanics, but it seems to me that a break-in should not be necessary. I think it might be in the porting.

<span style="text-decoration: underline">Help</span>: Does anybody know of a shop in the tri-state PA-NJ-NY area that is expert to review and fix this problem? (Assuming that my mechanic is wrong and all I need to do is drive it a few thousand miles)

Or should I buy a new W-DGV kit and try to do it myself and hope I get better results? There is one on eBay that is a complete kit with instructions. (This probably isn't the best solution - I set things on fire)

I'll be coming back to the U.S. in May for 12 days, and I would like to spend just one day getting this to work right before I head to St. Louis to pick up a hardtop I purchased for it. I am afraid the plugs will foul before I get halfway there.

Thanks so much for your help as we approach sports car season. - Dan
 
There's really no way to set a carb unless the ignition is adjusted properly. Start there first.

Do:
Points adjustment. Clean and adjust inside the distributor to make sure the advance is moving when vacuum is applied. Check rotor for cracks, replace with a known good one if available. Static set the timing. Clean off the plugs with brake cleaner and compressed air. Check gap the plugs and check porcelin insulators for cracks.

Then start the engine and let it <span style="text-decoration: underline">fully</span> warm up before touching the carb.
 
Hi Peter,

I should have mentioned that the points, rotor, and timing were all done. The plugs are new and gapped. All new heavy duty wires. New cap. I even tried two different kinds of plugs. What I was referring to above was a thought to change over to Petronix or something similar. It doesn't run rough, but it starts up with, again, backfire sometimes through the carbs.

What I did not mention was that the Webers were rebuilt by the mechanic in Kansas City who screwed up my engine rebuild. Perhaps the Webers themselves were rebuilt incorrectly by this guy? At $25/each for a rebuild kit, do you think it is worthwhile to rebuild them... again? It looks easy enough to do.

Thanks for your advice.

Dan
 
"Advice received: My mechanic, who I think is a mechanical genius, tells me I haven't run the car enough since its restoration and breaking it in may solve the problem. Maybe he thinks that after the engine has a few more thousand miles on it, the the carbs will work better."

All I can say is this sounds like pure BS. Does he want you to get as far from his shop as possible before you break down? The excessive fuel you have mentioned can not be good for your engine.

I suspect that something in your rebuilt engine is a problem, or, there is something with the carbs. Weber downdrafts do not seem to have a good reputation in connection with Triumphs.

I think you are doing the right thing looking for a different shop.
 
Yeah Tom, I have the SU's in a box waiting in the wings. I am thinking that is an option, too, but one guy I found on the internet told me to keep trying to get the Webers right because they give a bit more h.p. and are trouble-free (once working properly). I just got a name of a guy on Long Island, but hate to drive it all the way out there.
 
Back fire through the carbs is usually an indiction of retarded timing. You need to nail this down before driving and potentially hurting the engine.

Double check your static timing. Then check it with a timing light while the engine is running and see how/if the advance is working properly. When you rev the engine the mark on the pulley should move a little clockwise.

Stop the engine. Loosen the distributor clamp until you can barely turn the distributor with your hands. Then start the engine and advance it (turn anti-clockwise I think) just a hair. Advanced, the engine idle should come up a bit. Rev and check for backfire. If it sounds better, check the timing again with your light and note the behavior of the mark onthe pulley.

If the mark on the pulley is way off when you time it with a light, it's also possible that the engine builder messed up the cam timing gear alignment:

If it comes down to it, cam timing can be checked by removing the timing cover from the front of the engine. The two gears, one on the crank and one on the cam, should have a small dimple right up near the tips of the gear that the chain rides on. These should point to each other @TDC when cylinder #1 is fully at the top. If not lined up, the engine is not assembled to run as designed i.e. the cam timing is altered is relation to the ignition.

Doesn't sound like a beak in issue to me. Sounds like the timing is off.
 
Just so you know, there was a thread a while back on 6-pack where someone dyno'd a car with twin ZS and again with twin DGV. The DGV setup made quite a bit less hp than the ZS carbs.

nfi, don't shoot the messenger and all that...
 
I've had duel DVG's on mine for two years problem free...

when I put them on I had John from Quantum REJET them.

I'll try to find out excatly what jets he used.


(no fumes, no sputtering, No problems & trust me the HP is fine!)


a13.jpg
 
DGVs are a good setup, if, as Kodanja did, you get them jetted properly, as with any Weber. I have had two sets on 2 different TR6s and had no problems with them. They just are not noted for tuneablilty for high performance. Now, that said, Pegasus Racing catalog has a whole lot of parts and jets and such for the DGV, which apparently are used a lot on small Ford racing engines. Check-em out.
 
Are the carbs leaking fuel at all, is there any fuel hanging around the bottom of them when the engine is running? If there is then its likely the float or needle valve in the carb is set improperly or defective.
The smell of gas is a giveaway that somethings not right in the carbs. You will probably have to disassemble them to find the problem.
Backfiring through the carbs is usually a sign of incorrect ignition timing and that's where I would start. As PeterK stated there could be a cam timing problem particularly since that's been worked on recently but check the ignition timing first.
I would say you have more than one problem here and it's generally a good plan to get the ignition side of it right first then look at the carbs.
The break-in comment sounds like a crock to me.
 
Thanks all, I'll work on the timing issue. Now I have learned something that I couldn't find on my own. Backfire through the carbs is a timing issue. Chances are that it is in the gear alignment, but will recheck the timing as you suggest.

My best to you all.

Dan
 
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