|
Post by Trent on Mar 11, 2021 5:57:45 GMT 1
76 RD400C 2K Miles. Had engine rebuilt (Crank/seals/bearings and rebore/oversize pistons) after sitting in an office 42 years by a "reputable" builder. Engine starts, idles and revs through to the red line no problem. When you come off the throttle or just try to cruise along the engine surges so much its almost unrideable, worse than a badly tuned Kawasaki H2 Triple!! Before I go into this does anyone have any ideas of the cause of this? I heard the C had a tendency to do this apparently but this is ridiculous. One thing I have noticed is sealant of some type by the reed setup flange which is always not a good sign.... TIA
|
|
|
Post by headcoats on Mar 11, 2021 8:18:21 GMT 1
When i had it on my LC i had to increase pilot jet size
|
|
|
Post by rigga on Mar 11, 2021 9:12:35 GMT 1
Yes pilots too small
|
|
|
Post by reedpete on Mar 11, 2021 13:47:23 GMT 1
Two thoughts... Which pistons do you have fitted? The correct pistons have a small cutaway on the front skirt to allow a small amount of exhaust overlap. Maybe you have generic pistons ? Alternatively, it might be the pilot bleed passage that’s blocked, causing it to run lean, not actually the pilot jet itself which I assume has been selected as per the standard setup.
|
|
|
Post by Trent on Mar 11, 2021 13:58:39 GMT 1
Hi There, Thanks for that. Pistons are OEM Yamaha 2nd Oversize. Looks like a carb clean and check jets as a starter....
|
|
|
Post by chrisg on Mar 11, 2021 14:00:24 GMT 1
This is a common issue and much has been written on the AC site. The correct OE needles and pistons make a big difference. Make sure your chain isn't too slack as well. As mentioned, try pilot jet. You may need to play around for some time (but dont tell your wife) until you resolve the issue. Good luck.
|
|
ajh
Thrash Merchant
Posts: 415
|
Post by ajh on Mar 11, 2021 20:32:17 GMT 1
sealant might be a big clue as air leak at the Reed block( weak )might cause reving/surging
|
|
|
Post by reedpete on Mar 12, 2021 11:55:39 GMT 1
Trent, thinking about what you have not said rather than what you have said.....another common error is to use Reed rubbers and crossover tube from later bike. That also plays havoc with idle fuelling.
So as well as check carb internals for correct settings, do the same for all other Related items.
|
|
|
Post by wallcraft on Mar 12, 2021 14:41:47 GMT 1
Worn slides and carb bodies?
|
|
|
Post by Trent on Mar 13, 2021 15:58:38 GMT 1
Worn slides and carb bodies? Bike has only 2K miles. Was stored inside for over 40 years....shouldn't be worn parts there.
|
|
|
Post by Trent on Mar 13, 2021 16:01:31 GMT 1
Trent, thinking about what you have not said rather than what you have said.....another common error is to use Reed rubbers and crossover tube from later bike. That also plays havoc with idle fuelling. So as well as check carb internals for correct settings, do the same for all other Related items. Yes Thats what I was thinking. Never a good sign seeing that there. I think a good strip down of the carbs to start. Also a good look at whats going on at the reed blocks. The engine builder was of good repute, I can't understand why someone would do that. Thanks again....
|
|
|
Post by stusco on Mar 13, 2021 16:21:48 GMT 1
Worn slides and carb bodies? Bike has only 2K miles. Was stored inside for over 40 years....shouldn't be worn parts there. Must have had a bad seizure if its on 2nd oversize?
|
|
|
Post by Trent on Mar 13, 2021 16:30:18 GMT 1
No Bad seize apparently. The enginedid turn over and was sent for rebuild due to it being in an office for 42 years. The previous owner told me it was second oversize I havn't confirmed it yet. The obligatory Crank seals bearings all replaced. The engine builder thought it would perform better overbored but why he went second oversize I don't know. The builder was I said of some considerable repute and the build cost the previous owner $2000. Not an itemized bill just a Total dollar amount for some reason. Apparently thats how they worked together on many rebuilds??!!
|
|
|
Post by chrisg on Mar 13, 2021 17:30:04 GMT 1
Im thinking to remove the brass balls from the carb and ultrasonic clean, when off the bike.
|
|
|
Post by Trent on Mar 15, 2021 1:27:06 GMT 1
|
|