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Post by Doo640ER on Sept 13, 2020 14:05:44 GMT
o yesterday I got my latest addition running, the 77 TnT 340 f/a. Looks like it has primary clutch issues. I reved it up high enough that I would think the clutch would engage, but it really didn't move. I'm going to pull it off and give it a once-over and replace what's necessary. This has the Roller Square Shaft and I believe the Duralon bushing? I was doing some searching and I believe the correct part# is 504-2369 and/or 504-2280? What else should I be looking for on this clutch? This is my first actual experience with this type of clutch. Another issue I ran into was that the engine would not rev-up much at all. I spent a few days going through the fuel system. The tank had tar in it and I soaked it in industrial strength de-greaser which worked pretty good. Hot water rinses, gasoline rinses, repeat! What a mess, a great example of how NOT to store a sled, LOL. New fuel and primer lines, and a serious carb cleaning. I feel that I did a very thorough job on the cleaning. So I have a hard time believing that its a carb issue. Even the idle adjustment screw didn't change things much when I increased it. I'll try a fresh set of plugs today and see if that helps, I'm not convinced both were firing at all times and they were wet and black when I checked them. One side of the Y pipe may not have been as hot either.     |
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Post by bones on Sept 14, 2020 0:42:40 GMT
Have you checked to see if some rodents decided the muffler was a nice home ??
Bones
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Post by Doo640ER on Sept 14, 2020 23:40:17 GMT
Have you checked to see if some rodents decided the muffler was a nice home ?? Bones Hey Bones, I have not yet checked that, but it certainly was the next item on my list. I hope it's that simple and is the problem. I put a brand new set of plugs in it yesterday and started it up again and this baby idles really nice. Just a lot of bogging when applying any significant throttle .I'll report back after checking the exhaust for obstruction . Will it cause any issue to run the sled without the muffler for a minute or two? Thanks, |
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Post by bones on Sept 16, 2020 3:08:36 GMT
I am sure running with no muffler is no problem at all.
Bones
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Post by olyman on Sept 22, 2020 11:28:00 GMT
Wow good job on the carb clean! If you got all of the little holes clean too then that carb is good to go. If its still boggy with an open exhaust then check the rubber intake boot for signs of leaking. If that's good then check compression. I'd expect around 120 130 or so for that rig in good running condition. If thats good then check the seals by running and spraying ether around the pto.
Normal wear on those clutches is the rollers and the bushings. The rollers often get stiff and start sliding instead of rolling wearing flat spots on them. 'Nearly' impossible to make them roll again without sliding again. Bushings around the square shaft and where the arms pivot from are the other wear points. I think that engine used a light blue spring and C4L arms if I recall.
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Post by Doo640ER on Oct 15, 2020 17:24:32 GMT
So I was tinkering with this TnT a little over the previous weekend. Darn thing starts on the first pull and idles pretty nice. I noticed when it first started, it idled fairly high and I had to turn the idle screw down quickly. This is likely because when I had it running last time, the longer I had it idling, the more I had to increase the idle adjustment to keep it running. I could see some misty gas spiting out of the carb intake. Plugs are new and soaking wet. Opening the throttle barely helps it run at higher rpm, lot of bogging. Sounding like its flooded?
I pulled the muffler off to make sure there wasn't any obstruction. I hooked up a Shop Vac to it and there was absolutely no resistance so I'm fairly confident the muffler is clear. I also sprayed some brake cleaner at the PTO side crank seal and there was no increase in RPM. While I was trying to rev it up, I used the primer to squirt some extra gas into the carb and this just about stalled it out. Oh yeah, and compression was 150psi on both jugs when I went to look at it when buying it. That was with the PO's gauge, so I'll check it again with mine. Vince, the arms are C4L and one of the two rollers has a very slight flat spot on it. Is there a source for new rollers? The square bushing seems pretty good.
I'd like to rule out the carb as being a problem so I thought I might take the known good carb off my 81 Citation 4500 and swap it onto the TnT. Will it be OK for just a few minutes? Here are the specs compared to one another:
81 4500 is VM 34-256, 260 Main, 6DH4-3 needle, 159 P-0 needle, 3.0 Cutaway, 35 Pilot Jet, 1.5 turn air screw
77 TnT is VM 34-118, 300 Main, 6F9-3 needle, 159 Q-2 needle, 3.5 Cutaway, 35 Pilot Jet, 1.0 turn air screw
What doo you guys think?
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Post by olyman on Oct 15, 2020 18:27:22 GMT
I don't think you'll have a problem running it with that carb, just likely wont run right and end up making you mad. What's the condition of the rubber intake flange? The age of that one has got to have cracks in it by now. Based on you having good seals, good compression, good spark & plugs and a nice clean oem carb... I would consider that it could be still sucking air around or through that boot. I've had them go bad on several sleds. Even once on my 670ss a long while back when I was up north riding two up. Sounded funny when slowing down and idling different than normal. Shut it off right away and could see cracks on both boots when wiggling the carbs around. Out with the duct tape to limp home....
Dave Barnhill might have some rollers, and so might the Goose... With those clutches make sure the arms swing fully with no resistance and the arms have limited play.
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Post by olyman on Oct 15, 2020 19:35:30 GMT
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Post by Doo640ER on Oct 18, 2020 14:17:04 GMT
Hey thanks for the info Olyman, I got some success yesterday! I moved the jet needle to the most lean position and got the old girl actually reving-up. It still has a pretty noticeable bog, but I was able to rev it up and get the clutches to fully shift out. Filled the garage with some 2-stroke cologne. After running it for about 5-10 minutes I checked the plugs and they are still pretty black, but at least they are dry now. I've got a couple of Main Jets on order. Original is a 300, but I'll give a 280 and maybe a 270 a try (carefully of course). Oh, and I did check the intake boot and I see no problem with it.
So this begs the question: Why are the factory carb settings no longer applicable on this motor? Is there a problem I haven't discovered yet? What makes an engine run so much richer now than when new? I was contacted by a fellow member who said in order to get his same sled to run right, he had to jet-down three sizes and move his needle to the leanest setting. I doo understand that once it actually gets cold, it will run leaner.
I'm still learning every day with these old sleds. This is the first time in all these years that I've ever adjusted a Mikuni from it's OEM settings. Fun stuff, as long as I don't burn it down, LOL
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Post by bones on Oct 18, 2020 17:55:35 GMT
It appears there is no question you are running rich, ( which likely rules out air leaks ?).
I am sure you likely checked, but did you check the carb float height ?? Might be gonna need a new inlet needle/seat. If the fuel level in the float bowl is too high it will run rich.
Do you have the correct throttle slide ?? A 3.5 Doo style ?? Make sure someone didn`t install one from a different application and its the wrong rotation, as it must have the cut side to air box and none cut to engine. It is possible to install one that has the none cut to air box, then it is plenty rich.
My experience with them sleds is....You doo not need to stray from the OEM specs and it will run very nice. The only thing might be one or two sizes smaller main if its warm out or if you are on the big hills on the left coast.
The mid range/needle jets doo wear out, ( I have experience with this). I have had to change them with new at times to get a carb right as per OEM specs. I am a firm believer that OEM specs just plain work ( for pleasure riding).
I owned a 78 - 340 F/A for a while yrs ago. The carb had OEM secs. That sled ran flawless, once warm to start it, it was a flick of the wrist to start.
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Post by Doo640ER on Oct 19, 2020 12:32:42 GMT
OK, I've been thinking about this guys, and looking at what I did while I was inside the carb. Here is the original picture before cleaning and check out the position of the tab I have circled.
Now check out the cleaned version. I had to bend the tab pretty aggressively to get the float lever to sit level where I thought I needed it to go. It might be a problem with the needle? I just know that in the past I've never had to bend that tab the way I did when putting this carb back together. Think I'll yank the carb off and see exactly what's up with it.
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Post by bones on Oct 19, 2020 14:23:57 GMT
Looks like you might be onto something there Doo640ER. It sure don`t look right.
Bones
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Post by olyman on Oct 19, 2020 18:00:51 GMT
I agree. Maybe the last guy put the wrong needle in there? Borrow the whole assy from the other carb to see what happens & where it sits
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Post by Doo640ER on Oct 24, 2020 18:47:24 GMT
OK, I made some great progress today with my troubleshooting of this sled . I swapped the carb from my 81 Citation 4500 onto the 77 TNT. Wow!!! What a difference!!! It runs so good now that I almost took it for a spin around the pond. Responsive throttle and crisp. Plugs were still dark, but I saw a hint of chocolate brown. Really don't want to hurt this motor so I'm keeping a close watch. So I went to my storage garage and grabbed the carb from the other Citation 4500 I have. I've never touched this sled yet since owning it for a couple years now as it's another project for another day, LOL. That carb is all apart now and soaking in the cleaner. But here's a question I have: On the TNT carb, I noticed the location where the fuel retaining cup mounts is rough, sharp and jagged. Almost like it was sharpened like a knife. On the citation carb, it is machined flat and smooth. Could this be a cause for the crappy performance of the original TNT carb? Is it letting gas flow through where it's not supposed to go? Calling all you Mikuni experts!!   |
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Post by Doo640ER on Oct 24, 2020 22:22:33 GMT
Ok, next update. Might want to disregard my previous post? I took the good inlet needle and seat from the Citation and installed it on the TNT Carb. Still bogging at 1/2 throttle, runs terrible. Then I removed carb again and took the 260 main jet from the Citation carb and installed that on the TNT carb. Seems to run great now. But, Might be a different story once the airbox is installed and it gets cold and snowy.
Good practice for when I join a race team. I can remove the carb and switch jets in about 4 minutes.🤣👍
I still don't like it. Would it be best to just replace all components with OEM Mikuni? The need for a smaller main jet is masking something, and I don't want to get bitten! The actual carb body hasn't worn out, right?
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