Cuts out BAD and overheats

[fasterjimmy]

My first message. I recently bought a very nice & clean 77 cb750k on ebay. It was just as it appeared in the photos. The seller told me the previous seller had put these items on it. A 4 into one pipe, a Dyna.... electronic ignition system and accel coils and wires with hotter NGK plugs, individual air cleaner pods, and rejetted the carbs. This is my problem now.. the bike had no power and mis-fired badly at freeway speed and overheated. I pulled the choke and saw some minor improvement.. I pulled the float bowls and found the jets were #110's. Honda put 115's in it stock so he went the wrong way. I put in a set of 120's and it got better but still overheats. When it overheats it starts misfiring and eventually will quit. I let it cool for 5 minutes and it starts and runs ok. I put in a set of 140's (dealer was out of 130's) and it misfired like it was too rich but still overheats and quits. I found and installed a set of 130's and went for a freeway ride.. same thing... it overheated and quit.
I suspect I have tha carbs about right - it pulled great right up to 80 mph.. at a steady speed it eventually got hot and started slowing down... then quit.
The air temp is about 80 deg.. I'm using premium fuel.. I put the stock air box back on..
Anyone know why it overheats? I don't see any white smoke. the engine has good compression..
any help would be appreciated.
fasterjimmy..

[zzster]

You were right on the jetting adjustment, you were running too lean..  Now you have a timing problem with that new after market ignition system.  Way adavanced will cause overheating.  Get a manual to go thru the procedure.
zzster

[bill3749]

 

fasterjimmy wrote

My first message. I recently bought a very nice & clean 77 cb750k on ebay. It was just as it appeared in the photos. The seller told me the previous seller had put these items on it. A 4 into one pipe, a Dyna.... electronic ignition system and accel coils and wires with hotter NGK plugs, individual air cleaner pods, and rejetted the carbs. This is my problem now.. the bike had no power and mis-fired badly at freeway speed and overheated. I pulled the choke and saw some minor improvement.. I pulled the float bowls and found the jets were #110's. Honda put 115's in it stock so he went the wrong way. I put in a set of 120's and it got better but still overheats. When it overheats it starts misfiring and eventually will quit. I let it cool for 5 minutes and it starts and runs ok. I put in a set of 140's (dealer was out of 130's) and it misfired like it was too rich but still overheats and quits. I found and installed a set of 130's and went for a freeway ride.. same thing... it overheated and quit.
I suspect I have tha carbs about right - it pulled great right up to 80 mph.. at a steady speed it eventually got hot and started slowing down... then quit.
The air temp is about 80 deg.. I'm using premium fuel.. I put the stock air box back on..
Anyone know why it overheats? I don't see any white smoke. the engine has good compression..
any help would be appreciated.
fasterjimmy..

I've got exactly the same problem on my 78, but it doesn't seem to happen all the time. I did the e-ignition thing also (Dyna). Maybe it is a timing issue. Mine runs great then starts to misfire, popping and missing, loses power, and eventually just quits. If I down shift and roll on it will pick up but then starts all this mess over again. Let me know what you find out.

BC

[bill3749]

Check these guys out. Great forum: www.forums.sohc.net

[machine head]

hey what up?a little info for you.take stock air box of put #40 slow jet across then put #120 mains in the middle carbs and 117.5 jets on the two otter carbs set iddle air screw out one turn put single air pods on and i think you will like the improvment.and put a stock plug in like a ngk d8ea.sorry forgot that part.

[terry877]

i have the same problem my new tech tip is that the float bowls are not filling up when you get hard on the throttle