1979 Tight Valves, Cam Damage, How Bad Is It?

[millsmobile]

Could absolutely prevent firing. The air travel pulling fuel up the pilot jet is very low. You need far more air to move fuel out of the main jet. Sounds like taking the carbs out was a smart move, nicely done!

So actually they were backwards on #3 also, but that one had at least a little fire based on the plugs. Also the gasket between the vacuum bowl and carb was upside down on two of these. Will put them back on the bike to try instead of eBay haha. We'll see : )

 

[brettp]

Glad to see you found an these problems. Would have made you insane of you tore down the engine just to see it behave the same after reassembly !

 

[millsmobile]

Glad to see you found an these problems. Would have made you insane of you tore down the engine just to see it behave the same after reassembly !

Yes I'm glad I found them too, but those carbs were not involved in the reassembly plan haha.

I got it running and there's good fire on all 4 cylinders. I can see why these run like poo with the pods, I ran it a bit without any filter at all to check the throttles weren't sticking (idle was higher than Snoop) and you can see the slides violently oscillating up and down at steady RPM. Based on everything else I've found so far I still suspect this motor might be a mess inside. Pretty good clank, and it's obviously leaked quite a bit of oil in it's lifetime. Also when I ran it on the center stand, it seemed like it took an awfully long time for the oil to return to the crankcase.

 

[brettp]

My 1981 has 45k miles on it and it makes a bit of upper end noise. I hear that is normal. If yours is above normal (subjective determination, I know) maybe an oil pump is in order.

 

[millsmobile]

Here's said clack, sounds like the #1 area

My 1981 has 45k miles on it and it makes a bit of upper end noise. I hear that is normal. If yours is above normal (subjective determination, I know) maybe an oil pump is in order.

Yah kind of hard to tell right now since I went from running on two cylinders to running on four haha. I might consider trying an airbox if I can find the right stuff to put it on, but really I'm kind of leaning towards full send.

 

[dirtdigger]

If you have an upper end noise it probably has broken chain guides.

 

[millsmobile]

Update: got the RS34 from Ken & Suzi at Cycle X, 10/10 would recommend. I described the exhaust system to them and the current condition of the bike, and they sent the carbs jetted and ready to go. Install was easy. Bike fired right up with a little bit of choke, and the only adjustment needed was a 1/2 turn of idle after the engine warmed up.

If you have an upper end noise it probably has broken chain guides.

This was a great reminder, thank you. I had noticed there was a missing bolt in the guide and already had it on order. I had to loosen the other three bolts pretty significantly to put it in before tightening them all down again.

 

[millsmobile]

Soooo... it still seems like this motor needs a teardown, but I'm open lol. I've put a couple hundred miles on the bike. I replaced the battery, and also the regulator after it died mid ride last week. Starting it is hit or miss. As the engine warms up, the idle continues to rise and sometimes quite randomly. Thankfully this is really easy to adjust on the fly, but affects starting the bike next time. It pulls like bananas at wide open throttle, but at partial throttle it sounds a mess, and there's a fair amount of backfiring when engine braking. I've also had a couple of really impressive backfires while starting, and there's been two instances of a decent amount of smoke coming out of the crankcase breather. Yesterday I ran a compression test again to see if things had improved after putting some miles on, and I got 155, 155, 60, and 90. #3 was 110 before, and no change on #4. I'm thinking either a couple valves got toasted due to the tight clearances, or some rings are burnt / broken but it seems like it's time to pull it apart and find out.

 

[millsmobile]

This is what the plugs looked like yesterday when I pulled them out for the compression test.

 

[brettp]

I'm not a plug expert but I think all of those are within a good range. I can't tell if there are any deposits on them in the pics but they look ok.
That compression is really low. I would definitely check valve clearances again before tearing the engine down.

 

[millsmobile]

I'm not a plug expert but I think all of those are within a good range. I can't tell if there are any deposits on them in the pics but they look ok.
That compression is really low. I would definitely check valve clearances again before tearing the engine down.

Yah they seem good to me too. I'd suspect maybe just a little on the hot side but my MPG says plenty of gas is going in there.

Had a weird one yesterday, and actually 2nd time it's happened. Bike didn't want to start, wouldn't catch at all. Full choke, tried adjusting idle up a bit, throttle position, give it a minute, all that. So I pulled plug #1 to do a spark check and it fired right up on 3 cylinders lol. Put the plug back in and coaxed it to life. Some kind of vapor lock?

 

[brettp]

That is odd. I wouldn't go so far as to say cylinder 1 is causing the issue. But I would say it might be worthwhile to check all the wiring from the coil inputs and ground to the spark plugs. Look for poor connections due to corrosion.

 

[millsmobile]

That is odd. I wouldn't go so far as to say cylinder 1 is causing the issue. But I would say it might be worthwhile to check all the wiring from the coil inputs and ground to the spark plugs. Look for poor connections due to corrosion.

Yesterday it was also playing hard to start so I pulled #1 to see if it was repeatable, and lo and behold there was no spark. Not sure what changed other than cycling the ignition key off and on, but the 2nd time there was spark and it started quickly on 3 cylinders again. I'm kind of suspecting the ignition switch, however all the other electronics were functioning when there was no spark. I took the switch out of the electrical box and there was some corrosion around it which I cleaned, however also the switch functioned out of the box without a ground at all. The other connections look good, except when wiring the tach I did notice that the coils share a ground wire. Not to the same spot, like coil one is wired to coil two negative, and then number two is wired to ground. I'm assuming they should both have their own ground and not be in series like that, so next time the tank is off I'll wire that up.

 

[brettp]

Mine are grounded like as well.

The difference between the last time and this time is you pulled the plug and moved the cables. If there is corrosion in the coils' plug wires, moving them around can really in recreating a connection through the corrosion, or removing the connection by going into the corrosion. I'm telling you, pull the plug wires from the coils and the plugs and look for corrosion. You also want to run resistance checks on the wires and coils themselves.

 

[millsmobile]

Mine are grounded like as well.

The difference between the last time and this time is you pulled the plug and moved the cables. If there is corrosion in the coils' plug wires, moving them around can really in recreating a connection through the corrosion, or removing the connection by going into the corrosion. I'm telling you, pull the plug wires from the coils and the plugs and look for corrosion. You also want to run resistance checks on the wires and coils themselves.

Will do. The bike didn't come with many extra parts, but it did come with new boots for the plugs. Maybe there's a reason for that haha. Thanks for your help!

 

[Bo82CB]

Will do. The bike didn't come with many extra parts, but it did come with new boots for the plugs. Maybe there's a reason for that haha. Thanks for your help!

Hey wires, plugs, boots are cheap… I can’t remember from whom but They sell whole kit which includes all the stuff above for like $30!

 

[brettp]

Hey wires, plugs, boots are cheap… I can’t remember from whom but They sell whole kit which includes all the stuff above for like $30!

I bought a complete set from 4into1 for $60. I didn't want cheap Chinese crap and I hoped 4into1 wasn't. Happy with them so far.

 

[Bo82CB]

I bought a complete set from 4into1 for $60. I didn't want cheap Chinese crap and I hoped 4into1 wasn't. Happy with them so far.

Stuff I bought was not Chinese junk, plugs were NGK, plug boots NGK as well, wires were of a good quality…just can’t remember from where I bought them!!!
I’ll try to find receipt, it was whole tune up kit and it was advertised as such.

 

[brettp]

Maybe vintagecb750?