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TR6 Sputtering at low rpm

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FR Burkhart

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After multiple attempts in my garage and a couple weeks at a local shop, I still have challenges getting my TR6 running smoothly. When starting from a stop, the engine sputters. The sputter decreases as the rpms increase but still there up to 2,000-2,500 rpms. Even freeway driving, I can feel an occasional misfire/sputter. If full out acceleration, no sputter. With the throttle wide open, runs beautifully up to 5,000 rpm. And, idles well at 900 to 1,000 rpm.

At this point - replaced alternator, coil, distributor cap and rotor (electronic ignition) and spark plug wires. Replaced the fuel pump with electric pump. Carbs have been stripped down with new gaskets, diaphragm and floats. Bypass valve diaphragm replaced. Checked for vacuum leaks.

Known problem is the brake booster - idle drops when brake pressed and a nice hissing sound. Rebuilt brake booster on order from Apple Hydraulics.

What am I missing?

Thank you any help.

Frank Burkhart
 
What year and is all the emission plumbing and vacuum system plumbing installed completely and correctly for that year ?
 
I see two places you did not say. On my 1973 TR 6 the Distributor fly weight plate was sticking. As for RPM say 3rd gear will it red line. The reason I ask is I worked on a car the muffler came apart and clogged up and would not let the run out RPM. What year TR 6 Madflyer
 
poolboy & madfly,
TR6 is 1975. Vacuum line in place with clamps at both ends. Emissions in place except for lines running from the carbon canister to the carbs. Ran up to redline in 2nd and 3rd, didn't push all the way to redline in 4th - transmission is Supra 5 speed. New stock muffler installed within the last year.
 
FR Burkhart said:
poolboy & madfly,
TR6 is 1975. Emissions in place except for lines running from the carbon canister to the carbs. .
Click to expand...
That could be a problem, depending upon which hoses you're talking about and what you did with them
There are 2 sets of emission hoses that connect the CARBS to the Carbon Canister.
There's the set on the carbs that share the connection with the valve cover and carbon canister....and there are those on the carbs that connect the carbs' float chamber vents with the carbon canister.
Depending upon how you changed or 'modified' those connections, you could have introduced some problems with mixture and/or fuel distribution inside the carbs.
A picture of what you have would be helpful.
 
Picture 1975 TR6.jpgattached. Two more clues. Disconnecting the brake booster (sealing the ends) didn't make any difference. Also didn't make any difference to braking feel - replacement booster due later this week. Better clue - definitely more power and no sputtering with the choke out 3/4 of the way to max even after the engine was hot.
 
I can't tell if the small nipple on the intake manifold's Banjo fitting is capped or not. I do see a segment of hose on thet nipple but I can't tell if it's sealed or not...It should be sealed since it's not being used to supply vacuum to an Anti Run-on Valve....never mind I think I see something red plugging the end and that's OK if it's a tight fit.
AND I can't tell where the leg of that large hose that connects the carbs to the valve cover ends up. Can you describe or supply another picture of where it ends ?
The open to atmosphere hoses attached to the carbs' float chamber vent isn't related to the problem, though.
 
The large hose goes down to carbon canister. Tomorrow working on the fuel supply. With a few adjustments to the carbs, reduced the sputtering - until I took it for a short drive on the freeway. After a couple miles at speed, the sputtering came back with a vengeance. Back onto the freeway to get back to the shop, ran well at 2,000 rpm on the freeway but as soon as I got off and stopped at a light, the engine died and wouldn't restart. After waiting for about 30 seconds, engine fired right up and idled fine. Sputtered the last 1/4 mile. Although I installed a new, electric fuel pump a couple months back, thinking this may be a fuel supply or fuel pressure problem. Going to re-install the Triumph mechanical fuel pump to see if anything changes.

Thank you for all your advice and help. Let me know if you think the fuel problem is a red herring. Although it is cool in California, still great Triumph weather.
 
OK. you might want to make sure the vent hose from the fuel tank to the carbon canister is free of obstructions.
If you open the gas cap and pull the vent hose off the carbon canister and blow into the disconnected end of the hose, it should not take much effort to blow air clean thru to the gas tank... If there's an obstruction it's usually just a slug of gasoline laying in the belly of the vent hose. To clear that out, you might need a shot of compressed air.
 
You say full choke runs better says lean and or vacuum leak, at idle taking valve cover cap off RPM should change what happen with your car?? Madflyer
 
After more work and more testing, have a new theory. After installing a new mechanical fuel pump, during a test drive when the car sputtered to stop going up a small hill, in checking the fuel filter I noticed that it only had a minor flow of fuel, no where near half of the filter. Next week going to replace the line between the fuel tank and fuel filter and also drain and clean the fuel tank. And final step of replacing the brake booster with a replacement booster from Apply Hydraulics. Maybe by 2021 we will have a reliable TR6, just in time for the rains to start.
 
Hello, I'd be getting rid of the electronic ignition. Refit points and condensor. I've had similar probs and now have the opinion that everyone with electronic ignition shold go back to Kettering ignition. In theory, electronic is better, ie low maintenance, longer dwell, higher voltage output etc but most are unreliable!
 
robmate said:
Hello, I'd be getting rid of the electronic ignition. Refit points and condensor. I've had similar probs and now have the opinion that everyone with electronic ignition shold go back to Kettering ignition. In theory, electronic is better, ie low maintenance, longer dwell, higher voltage output etc but most are unreliable!
Click to expand...

Robmate - IMO that's a bit strong, given the build quality of today's condensers and coils. I've been running Pertronix I and II in my Healey for years. My '74 TR6 distributor was converted to advance and overhauled (British Vacuum Unit) within the last few months from originally a Pertronix I to a blue-wire condenser. The car has recently developed a flat-spot on acceleration from stop when hot. I'll be replacing the condenser first with a yellow-wire from Distributor Doctor, then the coil with a known-good Pertronix coil. Eventually will install a blue Brazilian Bosch coil.

PS - Frank - make sure the internal ground wire connecting the moveable plate to distributor body is good. Sometimes they have internal breaks causing a vibration miss.
 
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With a clear filter say glass one it will only seem as 1/2 full as it has a air pocket. Keep looking. Madflyer
 
My new (to me) 1970 TR6 had a similar issue the first time I took it around the block. Would idle fine, but would sputter when just starting to accelerate under load. I just acquired a carb synchronization tool and thought it was a good opportunity to try it out. I found the carbs notably out of sync. After adjusting, the sputter went away.
 
Evander,
Thank you for the tip. Am sure my '74 has the same issue.

Have peripheral cracks in my diaphragms so have ordered new diaphragms and a fuel pump. Will add the carb sync to the process when I get the new diaphragms installed.

Will report back then.
 
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