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Trouble Starting GT6 After Carburetor Rebuild

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ANDYGT6 Avatar
ANDYGT6 Andy K
SF East Bay, CA, USA   USA
I’d greatly appreciate some help from the wisdom of the Triumph crowd! I’ve read many posts and articles about all kinds of carburetor related items for my GT6 but am still in need of some guidance for my particular problem.

Problem is I can’t get my 72 MK3 GT6 to restart after rebuilding the carbs (ZS 150 cdse, Manual choke). The car was running reliably before I did the rebuild but after constantly missing dashpot oil, I decided to rebuild the carbs while they were off rather than just fix only the dashpot oil o ring issue. After the rebuild, I mounted the carbs and the car restarted but had fuel running out the emissions bypass valve at the bottom of the rear carb once I shut the car off (didn’t let run long). Seemed this would be float setting measurement too low causing overflow before the needle valve shut off the fuel. Took the rear carb off and adjusted the float to about 16.3mm (it was just a tad over 15), reinstalled, and car won’t start. Hit it with starting fluid and the car ran only until that burned off. So, now I’m thinking I may have made the float measurement too high, so off with the carb again. Measurement still checked out so tried swapping the old needle valve back in in case new one might not be good. Same result...will run on starting fluid but not continue to run. Hit the gas and it runs a couple of seconds longer before backfiring and dying. There’s fuel in the bowI and the floats didn’t have fuel In them when I was rechecking things. noticed float levels on the carbs before rebuilding were low compared to 16-17mm....between 14-15mm. So tempted to next readjust them back to a lower than 16mm setting to allow more fuel though seems I’d have fuel running out the bypass valve again. Have seen a couple posts that seem to suggest float levels in manuals are just a suggestion.

Appreciate any expertise on what to do next. Besides what I already explained, I replaced the metering needles with new ones from Rimmer Bros, making sure they were flush to bottom. Pistons drop in carb with audible click and seem aligned. Not thinking anything here to play with there just to get the car to run. Rather, waiting to adjust those further once car running.

Other things to check?

Thanks!
Andy

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trrdster Avatar
trrdster Wayne Tate
Spencer, NC, USA   USA
Andy, that's a bummer.
I would have to guess a major air leak. I think the gasket between carb and manifold has a little indentation and has to be in the right place.
If you hold a tissue up to the carb will it suck it toward the hole?
Just drawing straws.



Wayne
1970 TR6
2000 Jaguar XK8
1949 Triumph Roadster 2000
1978 Spitfire (rust victim)
1971 GT6 (tarp covered for 12 years, rusted inside out)
1980 Spitfire (getting all the good GT6 parts, all poly suspension and Spax shocks)

jimbob1982 Silver Member Jim Dougher
Buffalo, NY, USA   USA
Andy, if you can start the car with starting fluid it’s too lean. Unless Someone has added adjustable jets you can’t make the jets richer or leaner. So your float height is critical. Carb rebuild requires cleanliness. The tiniest bit of dirt can make a float needle stick open. You can call me to discuss it’s easier to discuss steps you’ve taken etc
Jim (716) 316-3526. I just helped a buddy last weekend with the same problem

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Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, NV, USA   USA
Turn your bypass valves all the way closed until you get a good idle.

Lizzard d id
san jose, CA, USA   USA
When it started up post rebuilding and had gas leaking , did it seem to be running on all 6 cylinders ?

"SF East Bay" ? I need to go up to Oakley , are you near there ? I need to pick up an item at Oakley stern drive .



Edited 1 time(s). Last edit at 2017-11-27 09:27 PM by Lizzard.

ANDYGT6 Avatar
ANDYGT6 Andy K
SF East Bay, CA, USA   USA
Thanks, Wayne. Good idea to check for air leaks but I have to get it to run long enough to be able to check that out further. Will plan that as a next step once I get it to run.

ANDYGT6 Avatar
ANDYGT6 Andy K
SF East Bay, CA, USA   USA
In reply to # 1500197 by jimbob1982 Andy, if you can start the car with starting fluid it’s too lean. Unless Someone has added adjustable jets you can’t make the jets richer or leaner. So your float height is critical. Carb rebuild requires cleanliness. The tiniest bit of dirt can make a float needle stick open. You can call me to discuss it’s easier to discuss steps you’ve taken etc
Jim (716) 316-3526. I just helped a buddy last weekend with the same problem

Jim, yes, does seem lean. The jets are fixed. I was also pretty tedious about cleaning the carbs fully before reassembling, so seems further adjusting the floats might be first next thing to try. Would like to take you up on your great offer to call to discuss. Got out of work too late tonight to call from west to east coast, but will try you tomorrow to see if I catch you at a time that works for you. Thanks, Andy

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ANDYGT6 Avatar
ANDYGT6 Andy K
SF East Bay, CA, USA   USA
In reply to # 1500223 by Lizzard When it started up post rebuilding and had gas leaking , did it seem to be running on all 6 cylinders ?

"SF East Bay" ? I need to go up to Oakley , are you near there ? I need to pick up an item at Oakley stern drive .

Hi - Yes, seemed to be running on all cylinders. I’m in Oakland in hills off 13. So, can be on the way to Oakley if you go up 880 though would take you longer to get to Oakley. Problem I have at the moment is have to leave for a week long business trip to east coast in two days. Was disappointed I didn’t get to wrap this up over Thanksgiving weekend.

ANDYGT6 Avatar
ANDYGT6 Andy K
SF East Bay, CA, USA   USA
In reply to # 1500202 by Doug in Vegas Turn your bypass valves all the way closed until you get a good idle.

Hi, Doug- how would I do that? They don’t seem accessible the way they’re mounted to the carb. And, would doing that cause the car to start in first place or is a secondary item to try once I first get the car to run. Thanks

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scardini1 Avatar
scardini1 Gold Member Jim Moscardini
Great Mills, MD, USA   USA
1968 Triumph GT6 "Rocinante"
2003 Jaguar XKR "Kitty"
Andy: I'm kinda in Wayne's camp - air leak. You said it ran, but leaked fuel after the rebuild, and that you took off the rear carb to reset the float height. I'd focus on the stuff you touched getting that carb off and on again. And like Wayne mentioned, my first check would be the alignment of the gaskets and heat spacer between the carb and the manifold. Make sure those little bypass cutouts are all aligned and in the right place.

Also, disconnect and plug your PCV (or whatever it is that we call the thing). If it gets stuck open, it will mess up your starting air flow big time. Just eliminating as many variables as possible.

One other thing: When you opened the float bowl the second time, was there gas in it? (and of course, the front carb's float bowl as well?). The problem could also be coincidental fuel starvation - but I hate chasing possible "coincidental" failures (very low probability - you start chasing phantoms & smoke usually)

Lizzard d id
san jose, CA, USA   USA
In reply to # 1500239 by ANDYGT6
In reply to # 1500223 by Lizzard When it started up post rebuilding and had gas leaking , did it seem to be running on all 6 cylinders ?

Hi - Yes, seemed to be running on all cylinders.
If it were running on all six and then you just worked on one carb it wound make me think maybe that one carb is ok as it is . The should maybe fire on one good carb on a few cylinders .If you block airflow in the back carb and let the motor "run' on just the front carb will it fire up ?

I think I might try to raise the gas level in the float bowls as much as can be . That will enrichen the mixture . It should fire up even if somewhat rich .

Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, NV, USA   USA
In reply to # 1500240 by ANDYGT6
In reply to # 1500202 by Doug in Vegas Turn your bypass valves all the way closed until you get a good idle.

Hi, Doug- how would I do that? They don’t seem accessible the way they’re mounted to the carb. And, would doing that cause the car to start in first place or is a secondary item to try once I first get the car to run. Thanks

It eliminates a potential hidden vacuum leak. It should only open under the force of a spike in the intake vacuum which prevents backfiring.

Outfect Avatar
Outfect Dave B
La Sal, UT, USA   USA
1940 Ford N Series Tractors "Henry"
1951 Other Not Listed "SnowMan"
1979 Triumph Spitfire 1500 "White October"
1980 Triumph Spitfire 1500 "Tangerine Dream"
Andy,

Haven't heard anything about the chokes?

Did you install new kits in the bypass valves?

DaveInUtah

ANDYGT6 Avatar
ANDYGT6 Andy K
SF East Bay, CA, USA   USA
Hi All - I have finally had time to get back to the GT6 after the holidays here. Good news is I was able to use all the good advice here. Found I did manage to get one of the gaskets between one carb and the manifold on incorrectly, but also readjusted float levels in both carbs which seemed to resolve the overall problem. Bad news is it was running really great and I was doing the fine tuning of the carbs and also the timing. Was just about all done with it when just one more slight turn of the distributor to further tune the timing and the car suddenly died and won’t restart. Now I’m really stuck. Think I will start another thread for that issue.

jimgt6 Jim E
Seekonk, MA, USA   USA
Late to the party, I know but since this a 72 as is mine here is what the PCV hose routing should look like. There are also restrictors on the hoses going into the carbs. They look like white plastic hats and go over the brass tubes coming out of the carbs. the restriction is 3/16". TR6 restrictors look the same, but the restriction is 1/4" Bigger hole or no restriction can further lean out the mixture.

Jim


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