TR6 Carburetor issues at low rpms webers

[Firsttimer]

Im new to this car and am trying to determine if I am looking at the right thing to solve my problem. Car was idling way too high 1,200 to 1,400 rpms. Also was experiencing backfire, stalls and stubbles when taking off or whenever the engine was lugging. Ran great at higher rpms and pulled well. I started by adjusting idle screws and got idle down to 900 rpms. Took the car out and had a tremendous drive. No problems until coming down a small incline and then the car started bucking and backfiring when I stepped on the gas at bottom of hill. Limped it home coughing and sputtering. Idle was elevated to 1,200 when I stopped. I noticed only one carb actually seats on its idle screw, the other has a gap. Should they be set the same? Also seeing signs of too rich a mixture i.e. blackened plugs on 3 plugs with the other 3 looking good.

Where to start?

 

[TR3driver]

I would probably start by pulling those carbs for cleaning and inspection. Sounds like you may have something loose (perhaps only crud) that is moving around. That will also give you a chance to record which tuning components are installed (and make sure they are the same).

Or, start looking for a set of standard carbs. Webers have an undeniable bling factor, but stock SUs or Stromberg's will be far more reliable, require less fiddling for changes in altitude, etc.

You might also mention which Webers.

 

[CJD]

I don't know how Webers adjust...

...but your symptoms are spot on for a severe lean mixture, and therefore most likely due to a vacuum leak somewhere. I am assuming the "backfiring" is through the carbs. The rich signs come from the missing, backfiring, and acceleration circuit trying to compensate.


If the backfiring is from the exhaust...then you also have an intermittent ignition problem. Fix the ignition problem before trying any troubleshooting on the carbs.

 

[TomMull]

+ 1 on the ignition.
As for idle stops, both carbs should be set independently with the linkage disconnected. Then re-connect.
https://www.piercemanifolds.com/category_s/311.htm
Tom

 

[Firsttimer]

Thanks for the input. The backfiring seems to be in the carbs and you can cause a backfire by reving the car quickly. Now that Winter has set in I probably could do a deep dive into the carbs themselves, since I won’t be driving it anyway. I’ll try to locate any vacuum leak but the connections look fine to the naked eye. Not sure which Weber’s as it is very difficult to see any numbers or work on them because there is so little room between them and the inner quarter panel wall. Looking down into the bodies I see the two jets show a 160 and 165 in each.

 

[poolboy]

Do they look like this ?

 

[Firsttimer]

Yes Poolboy I would say they do.

i don’t know if they were a good choice to replace the original carbs. I do know that I have been averaging around 12 mpg on my first several tanks of fuel which seems low to me.

Any insights on these carbs is appreciated.

 

[Tybalt]

What you have there is a pair of Weber 32/36 DGV carbs. I'm more used to playing with the DCOx series and not all that familiar with the DGxV series, but they still follow the basic Weber parameters from what I understand. Here's some stuff pulled from Top End Performance's Weber info page:


Step-1: If you are having a problem with how the engine runs...Poor idle quality, stalling, etc then this is the first thing to do. CHECK FOR VACUUM LEAKS ! This is particulary true of new installations where you just purchased and installed a conversion kit and you are having problems. You have to remember that most Weber conversions have been around for many years and have been installed on hundreds of cars and trucks. They work. The likelyhood of having a defective carb out of the box is about like being hit by lightning. If you are having a problem on a new install it is most likely this problem or one of the steps below... See the Vacuum leak tech page for this info. DO NOT OVERLOOK this as a problem...This is the #1 problem with any Weber carb conversion.

Specific Information on Mixture Screw Setting for:
32/36 DGV, DGEV Carbs. If you have to open the mixture screw more than 2 turns on a 32/36 DGV or 38 DGES your idle jets are too small...If you have to shut them below 1/2 turn they are too big....

IDF carbs are similar to the DGV and DFV series in that the air is mixed internally. There is no F Number (comment, that's only for IDA and DCO, DCOE, DCOM units) to deal with. The IDA carbs have no Air Bleed Hole but do have an F number to identify this feature. It is an F10. The Air Bleed for the IDA carb is in the Idle Jet holder and it is metered similar to the DCOE. For those of you with multiple IDA or Rotary engines running a single 48 IDA you usually know what you are doing so I won't go into all the details on this.,..

Idle jets are in .5 steps...50,55,60,65 etc. The bigger the Idle jet number the richer the jet. 1 step in idle jet size can make a HUGE differerence. Do not go up or down more than 1 step at a time when tuning the idle circuit.



32/36 DGV, DGEV, DFV and DFEV:
These carbs have fixed venturis so the choke size is not an issue. The pump jets are also not a problem. Do not mess with them. If you have a flat spot or hesitation when you first take off then it is likely that the idle circuit is too lean. If you know you have the idle circuit right then the primary main jet is too small. Increase the main jet size 2 steps at a time. (150 main is a 1.5mm hole...Main jets are in steps of 5. eg: 150, 155,160,etc.) Keep checking the plugs after driving it for a few minutes (Do not let it idle when checking the spark plug color for the main jets. Drive the car above 2000-3000 RPM for a few minutes then shut the engine off before letting it idle then check the plugs. If the car then transitions fine but hesitates or falls on it face when the secondary is opened you need to work on the Secondary main jet....
A good option to playing around with your 32/36 Weber jetting is to just get one of our Custom Performance Jetting Kits....We offer these for all Single 32/36 DGV and DGEV applications operating from Sea Level to approx 4000 Ft...Above 4000 Ft you start having more altitude problems and the vehicle needs to be tuned as outlined here. Another good option is to install a Halmeter AF30 Air Fuel Ratio Gauge to help you with tuning. It is fast and accurate and will take alot of the guesswork out of it. This is a particularly valuable tool for cars that get track use so that you make sure you do not lean out and put a hole in a piston...



URL for page: https://www.racetep.com/manufacture...ning-downdraft-and-sidedraft-weber-carbs.html

Best wishes on sorting this out.

 

[Firsttimer]

Checked for vacuum leaks. I only forund one vacuum hose connected from one carburetor to the distributor. The second carb has a cap over the vacuum connection with no hose going anywhere. Is that the correct set up?

 

[poolboy]

You'll need to start the engine and see if the carb is creating significant vacuum within that hose..so start the engine remove the hose from the distributor and if you don't have a vacuum gauge, just see if there is enough vacuum to hold onto the tip of your finger with suction while the engine idles.
If it is it's OK but not necessary to have the hose connected to the vacuum RETARD module on the cockpit side of your distributor.
You might run the same test on the capped nipple on the other carb and see if there is suction there.
I may already have already confused you by saying this :"it's OK but not necessary to have the hose connected to the vacuum RETARD module"...but that can be a topic for later..."to Retard or Not".

 

[TR3driver]

What year TR6 is this?

Those carbs almost certainly will only have a port for ignition advance, which is quite different than the port for ignition retard. (Which means it should flunk the test that poolboy gave.) Early TR6 did have vacuum advance, but later ones only had vacuum retard (as original).

My suggestion is to disconnect and cap the port, then set the ignition timing to the "static" value from the book (typically 10 or 12 degrees BTDC, varies by year). See how it runs, solve the other problems, etc. Then later, if you want, you can worry about getting the vacuum retard working. The retard adds nothing to performance, is strictly an emissions thing (and not a very good one at that).

Note that one hidden source of vacuum leaks is the power brake booster.

 

[Alfred E. Neuman]

Note that one hidden source of vacuum leaks is the power brake booster.

+1 on this as a sneaky vacuum leak area. Best way to tell is to have a vacuum gauge hooked up in line with the hose to the booster and see if vacuum falls when you hit the brakes.
Easy to spot on an old Merc 123 diesel. If the engine wont shut off with your foot on the brakes, but does if you take your foot off = bad booster.

 

[TR3TR6]

I have weber's on my 76 TR6, I have a vacuum line running from the rear carb (closest to the firewall) to the vacuum advance. The front carb I have plugged. I have pictures here if I can get them to load. I have another vacuum line running from the brake booster to a vacuum gauge on my dash also in the pictures.

 

[poolboy]

You say you have a "Vacuum Advance" ?
Did you have the retard module removed and replaced it with a vacuum advance module ?...I ask because with an original unmodified 76 distributor, in fact any distributor on a TR6 from 72 on, only had a vacuum retard module....

 

[STeve 1958]

There is a great tendency to blame the carburetors first. I wouldn't even mess with the carbs. until you check out all the electrical system. A lot of your symptoms sound like timing issues. My TR3A came without vacuum advance or centrifugal advance. After I tuned the carbs. to no avail, I rebuilt the distributor. What a difference. Of course I had to start over on tuning the carbs. once the spark was right. Today was my first drive and I learned a lot so I can re-adjust a few things. (retard the timing a bit)

Also I had a GT6 where the wire connected to the coil would work loose and cause missing. Check that.

 

[TR3TR6]

Good question Poolboy, after looking at the distributor it is a retard module. Everything works good with this hookup, idles at about 750 RPM's. I should have taken a picture of the distributor. I put these carbs on myself and have had no issues.

 

[poolboy]

This is what the conversion from Retard to Advance looks like.
Notice the module is on the Retard (cockpit side) side of the distributor, but see that it's vacuum nipple is not; it's on the opposite side of the module's diaphragm and the vacuum itself comes from a different source.
You can read more about it, if you're interested, here:
https://www.britishvacuumunit.com/ported-vacuum.html

 

[TR3driver]

If you have an advance port plumbed to a retard module, the engine may still run "OK", but you're losing fuel mileage, and if you set the timing to spec (4 ATDC), performance too.

The 4 ATDC figure assumes the retard module is connected and giving around 15 degrees of retard at idle (throttle closed). But the advance port doesn't supply vacuum at idle, so the module won't be giving retard and you've just set the base ignition timing way too slow. The whole point of varying ignition timing is to get the peak cylinder pressure timed to match the most advantageous crankshaft position. With timing too late, the piston has already moved down the cylinder and less power gets used to turn the crankshaft. The rest goes out the tailpipe.

Then at part throttle (ie cruising at a constant speed), the advance port DOES supply vacuum, retarding the spark even further. Again, throwing power (and fuel) out the tailpipe.

 

[TR3TR6]

Poolboy, that sure doesn't look like mine, see picture.

 

[poolboy]

But Terry, notice the nipple on yours is on the cockpit side of the module which draws the points counterclockwise retarding the ignition when vacuum is applied.
The conversion on mine has the nipple on the forward side of the module which draws the points clockwise advancing the ignition when vacuum is applied.
Mine is the Vacuum Advance conversion you can read about in the link I posted in the previous post.