Newly rebuilt GT750 smoking R cylinder

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mfrias2nd
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Suzuki 2-Strokes: '75 GT750, '73 Norton...yeah I know, not here

Newly rebuilt GT750 smoking R cylinder

Post by mfrias2nd »

Hi Y'all,

any quick insight into my R cylinder smoking excessively after a fresh rebuild?

1975 converted to earlier VM carbs.
Original oil pump with older style lever
Bike hasn't run fully for a proper tune but all 3 carbs are tuned exactly the same
Newly rebuilt crank by Roy Gibson
Case halves sealed properly, no coolant leaks.
Pipes were drained of any excess oil prior to reinstalling
Compression checks out at 120 across all 3 cylinders
I haven't filled the trans with fluid yet, just trying to get it tuned up
hardly any smoke on L and C
Smoke seems to worsen with more throttle or longer time on.

Any thoughts would be greatly appreciated. I'm being very careful. a year ago while doing maintenance my ratchet hand slipped and I broke off the SRIS valve in the case. Had to pull the engine to remove, thankfully I also discovered that a crank seal failed and a seal spring was in a million pieces at the time it still ran but it wouldn't have survived a proper ride. Roy Gibson was the absolute man when it came to rebuilding my crank.

thanks, Mario
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jabcb
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Suzuki 2-Strokes: 69 T350 thru 75 GT750
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Re: Newly rebuilt GT750 smoking R cylinder

Post by jabcb »

Could be an ignition issue.
I use an old inductive timing light to check for good sparks when the engine is running.
And use a cheap Harbor Freight infrared thermometer to check header temp.

Don’t run the motor without the proper level of transmission oil. One of the crank bearings is lubricated by the transmission oil.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
mfrias2nd
On the street
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Suzuki 2-Strokes: '75 GT750, '73 Norton...yeah I know, not here

Re: Newly rebuilt GT750 smoking R cylinder

Post by mfrias2nd »

Thanks! I'll fill it the trans today!

I do have a newtronic ignition installed and I've done my static timing. I did read somewhere about spark plug gapping but I didn't know ignition would make that much smoke difference. I did forget to mention that when I pulled the plug a lot of smoke came out of the spark plug hole and the plug did seem wet.

Basically too much oil or not enough ignition. I'll check again. anybody know how to upload a pic or what type of pic I can upload? I have a 500kb image in jpg format and I get a "wrong format" error message.
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jabcb
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Suzuki 2-Strokes: 69 T350 thru 75 GT750
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Re: Newly rebuilt GT750 smoking R cylinder

Post by jabcb »

Upload your pics to a photo sharing website. I use Flickr, which is free.
Then include links to those pics here.

Both of my GT750s have the Newtronic ignition.
Had a plug cap problem on the gray GT750. Got so much smoke when I replaced the plug cap that my driveway looked foggy.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
mfrias2nd
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Posts: 45
Joined: Fri Jul 05, 2013 10:07 am
Country: U.S
Suzuki 2-Strokes: '75 GT750, '73 Norton...yeah I know, not here

Re: Newly rebuilt GT750 smoking R cylinder

Post by mfrias2nd »

Can everyone see the pics? and video, I hope.

https://www.flickr.com/photos/137748585 ... 30249RW23B
mfrias2nd
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Suzuki 2-Strokes: '75 GT750, '73 Norton...yeah I know, not here

Re: Newly rebuilt GT750 smoking R cylinder

Post by mfrias2nd »

UPDATE -

I pulled my R pipe - Full of oil
I removed the SRIS fitting - lots of oil came out and it was very viscous, leads me to believe I may have got some coolant in there. I left it disassembled to see if the drain pan gets more fluid. Tomorrow, if the drain pan has more fluid it's likely coolant and I have a weeping head gasket.

NOTE: When I torqued down the head after the rebuild I went to the lowest torque setting with the intention of going up. I had forgot and filled the engine with coolant and coolant started seeping through the head gasket. I drained it, torqued the head to full torque settings and refilled and no leaks. The coolant likely seeped into the crank case but now there should be no fluid. Unless the gasket is trash now and it's weeping coolant into the right side of the case.

ALSO - I mentioned that I have the M model oil pump still installed but I have the earlier lever so I could use the earlier style cable. Can anybody with the earlier model verify if I have the lever in the correct position - I have it pictured next to the older style (installed) in idle position the dash lines on the lever and oil pump should be matched but the earlier models state to adjust in full throttle position. I've added pics

https://www.flickr.com/photos/137748585 ... 1MZ3a8UzD6
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jabcb
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Re: Newly rebuilt GT750 smoking R cylinder

Post by jabcb »

Various manuals are here: https://www.oldjapanesebikes.com/mraxl_ ... /index.php
The GT750J owners manual shows how to adjust the oil pump.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
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tz375
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Re: Newly rebuilt GT750 smoking R cylinder

Post by tz375 »

If the oil pump were 180 degrees out, all three would be smoking, so that's probably not the issue.

Excess oil in one side is typically caused by an oil feed check valve leaking allowing that side to partially fill with oil. Remove the pump after you pinch off the oil pipe from the tank and see if the right side drains down.
Remove the oil feed system sometimes known as a spider or octopus and use a hand oiler to squirt kerosene through the lines to clean them out. Do not ever use compressed air because it causes the balls to end up inside the springs and take it form me, that's not good.

If you suspect ta a seal might be leaking, do a leakdown test. When you search on line for details be sure to click only on two strokes. 4 strokes are tested at up to 100 psi and two strokes at around 6 psi. Much more and the seals are damaged.
mfrias2nd
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Suzuki 2-Strokes: '75 GT750, '73 Norton...yeah I know, not here

Re: Newly rebuilt GT750 smoking R cylinder

Post by mfrias2nd »

:UPDATE:

after some more troubleshooting I discovered that the R pipe was full of oil after just a few seconds of running, I plugged the top fittings and ran the bike with the lower SRIS ports feeding into a drain pan and I got, what seems to be at least, excessive oil coming out of the R cylinder and quite a lot of leakage out of the pipes. They're chambers that are held on with springs so they don't seal the best anyway.

I also gapped the plugs to .028 and I also checked the timing with my timing gun, which works on 2 strokes and it seems to be spot on after doing a stationary timing with a dial gauge. I could really use some advise as to what to try next. Could my pump be set 180 too high? The videos show it all. Much appreciated everyone.

Please see the videos.

https://www.flickr.com/photos/137748585 ... bj9h992hPJ
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tz375
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Re: Newly rebuilt GT750 smoking R cylinder

Post by tz375 »

Time to remove the pump and oil feed and check the check valves. The easy way is to use a hand oil can to fill all the lines at the pump end and hang it up with manifold end up and banjo end down. Expect to see one or both of the right feed tubes empty themsleves.

To clean them out try kerosene or alcohol but do not apply air pressure because that will drive the check valve balls into the springs and then they will never work.
mfrias2nd
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Country: U.S
Suzuki 2-Strokes: '75 GT750, '73 Norton...yeah I know, not here

Re: Newly rebuilt GT750 smoking R cylinder

Post by mfrias2nd »

UPDATE

Got the feed lines removed. that the 2 feed lines most forward towards the engine and to the clutch side are draining. That is I think they're draining if they're not supposed to empty out at all under gravity.

Can you experts see my video and let me know if that is indeed a bad check valve and also let me know if there is an actual procedure to fix or replace these? Also, while I have the oil pump off is there anything else I should do to test and inspect?

As always your expertise is very much appreciated,

Mario

https://www.flickr.com/photos/137748585 ... 7hwTm8YB54
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jabcb
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Re: Newly rebuilt GT750 smoking R cylinder

Post by jabcb »

The oil leaked out pretty quickly. Try using something like a squeeze bottle with alcohol. This has worked for me.

It is possible to disassemble the problematic fitting. Have never tried it. If the alcohol flush doesn’t work, perhaps another forum member can explain how it’s done.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
mfrias2nd
On the street
Posts: 45
Joined: Fri Jul 05, 2013 10:07 am
Country: U.S
Suzuki 2-Strokes: '75 GT750, '73 Norton...yeah I know, not here

Re: Newly rebuilt GT750 smoking R cylinder

Post by mfrias2nd »

that video was done after I pushed some solvent through. I need to try and push solvent from the other way so I need to modify a banjo bolt or figure out another way. Either way I have 2 leaky check valves.
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tz375
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Re: Newly rebuilt GT750 smoking R cylinder

Post by tz375 »

Good news is that you have identified the problem. It's a common problem.

Use a banjo bolt and nut so you can push alcohol or other solvent backwards from the motor end to try to flush out those check valves. That is, fit the banjo bolt through two sealing washers and use a nut to hold it all in place and seal it, then push solvent into the open end of the banjo bolt.

If a prior owner used high pressure to clean the lines, at least one ball will be inside the spring and unable to seal.

Image



carefully remove the check valve and rebuild it or replace the ball and springs, but a replacement or fit a Kawasaki check valve.
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