Author Topic: GTR Carbs Not Functioning  (Read 1182 times)

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Offline davis

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GTR Carbs Not Functioning
« on: September 10, 2021, 08:56:53 AM »
Greetings all,
I am stumped on a real anomaly here. I completely disassembled my engine to solve three issues: low compression, oil leaks, and uncontrolled richness. After careful reassembly the first two were solved but the third ends up with carbs that essentially aren't working - no, or little, fuel being delivered to both combustion chambers. Although not dirty, both were disassembled, ultra sonic cleaned, and air blasted. Floats were reset and fuel delivery from the tank confirmed. The the engine will not start and no fuel is seen on the plugs or smelled in the spark plug holes or the end of the muffler. The only change made from the prior good running engine was inserting Moonpup's choke pads with new choke return springs. (A shout-out for his generosity). Choke function seems fine. I taped the carb inputs to encourage fuel delivery, which gave a backfire that blew the tapes off. Apparently enough fuel was delivered to give lean burn backfires(?) Any help would be appreciated since the season is drawing to a close and I would like a ride this year. I will keep you posted as to progress. Thanks - Bob

Offline BRT-GTR

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Re: GTR Carbs Not Functioning
« Reply #1 on: September 11, 2021, 03:03:45 PM »
   Hi Bob,
               Sounds like you sorted the uncontrolled richness, as well.  lol.

          Ok,  No fuel to cylinders - 1st thought - Disc valves 180 degs out, easy check, valves should be open at TDC, just about to close,  when viewed through the carbs.
      Beyond that, sticking float or float valve, although, unlikely to be both sides. Let us know what you find.
    Good luck,   Brian.
« Last Edit: September 11, 2021, 03:09:49 PM by BRT-GTR »
Unspoiled by progress.
I'm so glad I grew up in the 60s & 70s. I did so much stupid stuff and there's no record of it.............Anywhere !!

Offline davis

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Re: GTR Carbs Not Functioning
« Reply #2 on: September 12, 2021, 03:54:30 PM »
Picture shows T.D.C. on the left side with c.c.w. valve rotation. Thanks for your input Brian.

Cheers, Bob

Offline davis

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Re: GTR Carbs Not Functioning
« Reply #3 on: December 29, 2021, 03:56:16 PM »
I can close this one out, the bikes running great now.  banana  Besides a few oops on my part, I came to appreciate the high capacity of the oil pump. It seems the pump could supply oil to a 700 c.c. 2-stroke engine!

Special thanks to Brian who patiently offered his help throughout the whole process.

Offline Steve Swan

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Re: GTR Carbs Not Functioning
« Reply #4 on: December 29, 2021, 09:02:37 PM »
Hi Davis,

What did you find or do to remediate the richness, oil leaks and low comperession?

Kind regards

Offline davis

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Re: GTR Carbs Not Functioning
« Reply #5 on: January 07, 2022, 04:12:00 PM »
Richness: I followed Brian's example and changed the pilot jet from #22.5 to #25 and bought a die to correct threads to adapt to BS carbs. But I think the most important part was reducing the pump stroke to 1/2T out (3/4T is recommended) and reduced the cable stroke well below that specified. It still blows smoke, I'll keep an eye on it. That system really needs a method of gaging pump output. I suggested one to Brian but he didn't like the idea.

Oil leaks: I cut a groove in the shifter drum output shaft for an o-ring. This and thread sealant on the screw in it stopped the annoying leak through the shift selector indicator. Gasket sealer was used on the gaskets, except only on one side of the side covers for easier removal. Here I made sure the joints from the top and bottom cases were sanded level. And I cheated - Shell SAE 30W oil was used in the transmission. Don't plan to run in the winter or on the track anyways.

Compression: The cylinder base gasket area got special attention since the gland areas can be so small. Surfaces cleaned, smoothed, and levelled with pits epoxyed. New gaskets sealed both sides. Same with annealled copper head gaskets using proper head gasket sealant. Leak down test checked out. Was careful on case re-assembly because poor sealing between the crank case chamber and gear box could reduce cylinder pressures. 130 p.s.i. both cylinders.

Offline Steve Swan

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Re: GTR Carbs Not Functioning
« Reply #6 on: January 12, 2022, 01:46:51 AM »
Hi Davis, thanks for taking the time to share what you did to address the issues your bike was having.  Always good to learn what we do to improve how the bikes are running or fix issues that are a problem.

 


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