Re: 1981 CB750K - Repair/Tune-up
Posted by cdaiscool on Mar 21, 2012; 11:39pm
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/1981-CB750K-Repair-Tune-up-tp3846604p3847173.html
Carbs were sync'd by the local Yamaha dealer which also works on these bikes. Here's the full write-up from them on the bike's issues:
Recommendations:
1. The compression is low.
2. The front brake pads are worn out.
3. The front brake fluid is low. (WHY THE HELL DIDN'T THEY FILL IT??? Derp.)
4. The drive chain is rubbing on the center stand.
5. The right hand mirror is missing.
6. Wires are routed wrong under the seat and may short.
7. The left hand side cover is broken at its upper rear mount.
8. The right hand side cover is broken near the bottom mount and the piece is wedged in place.
9. The carburetors may need to be cleaned.
10. The compression is low and head gasket is leaking, the engine needs top end repairs.
Resolution:
Performed carburetor synchronization, found the vacuum to be very low at 3 in/hg and it is supposed to be 7 in/hg. Hd to turn the idle speed adjustment in about 2 turns to obtain proper idle speed. Performed compression testing and found with dry testing it was #1=75 #2=65 psi #3=70 #4=70psi. Wet testing results were #1=120 #2=95 #3=105 #4=100psi. Test results indicate the rings are at fault for sure and there may be other contributing problems with the low vacuum also such as restricted low speed jets in the carbs.
So... I've got some fun ahead of me. I've got mirrors coming in tomorrow, ordered up the brake master cylinder posted earlier, going to get brakes soon (was going to wait, but I'm pretty sure they are shot - I can just hear 'em grinding) and need to figure out the center stand issue. Then it's do the wiring and I'm good. Except for a carb cleaning and top end rebuild.
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/1981-CB750K-Repair-Tune-up-tp3846604p3847173.html
Carbs were sync'd by the local Yamaha dealer which also works on these bikes. Here's the full write-up from them on the bike's issues:
Recommendations:
1. The compression is low.
2. The front brake pads are worn out.
3. The front brake fluid is low. (WHY THE HELL DIDN'T THEY FILL IT??? Derp.)
4. The drive chain is rubbing on the center stand.
5. The right hand mirror is missing.
6. Wires are routed wrong under the seat and may short.
7. The left hand side cover is broken at its upper rear mount.
8. The right hand side cover is broken near the bottom mount and the piece is wedged in place.
9. The carburetors may need to be cleaned.
10. The compression is low and head gasket is leaking, the engine needs top end repairs.
Resolution:
Performed carburetor synchronization, found the vacuum to be very low at 3 in/hg and it is supposed to be 7 in/hg. Hd to turn the idle speed adjustment in about 2 turns to obtain proper idle speed. Performed compression testing and found with dry testing it was #1=75 #2=65 psi #3=70 #4=70psi. Wet testing results were #1=120 #2=95 #3=105 #4=100psi. Test results indicate the rings are at fault for sure and there may be other contributing problems with the low vacuum also such as restricted low speed jets in the carbs.
So... I've got some fun ahead of me. I've got mirrors coming in tomorrow, ordered up the brake master cylinder posted earlier, going to get brakes soon (was going to wait, but I'm pretty sure they are shot - I can just hear 'em grinding) and need to figure out the center stand issue. Then it's do the wiring and I'm good. Except for a carb cleaning and top end rebuild.
Turbos, Hondas, 4-bangers, what could go wrong?
Shiny: [...] Considering the weather you've had to put up with I'd say you get an Iron Butt award and a Frozen Nipple trophy to go along with it. First time I've ever posted the word nipple... it ends here.
Shiny: [...] Considering the weather you've had to put up with I'd say you get an Iron Butt award and a Frozen Nipple trophy to go along with it. First time I've ever posted the word nipple... it ends here.
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