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I'm sure this question has been asked before and searching on the forum has given me so many different answers that I have no idea where to start. I recently purchased a '78 Honda CB750F SS. Since it's purchase, i've had a hard time to get it to idle. On a cold start I have to pull the choke and sometimes it starts right away sometimes it doesn't but it usually has no problem starting with the choke. RPMS with the choke on are about 1200-1400. After I get it warmed up for a bit I take the choke off and the RPM's drop to about 1,000 or so. Then it starts to sputter and dies. I've recently cleaned the carbs out twice and they were pretty damn clean to begin with. Looks like the PO took them to a professional since all the slides and parts are nice and shiny with no gunk/blockage. I've also taken the plugs out and they were all black. Someone told me it was running too rich. So far I've heard it could be several things. Could be vacuum problem, mixture screws need to be turned out more to make it more lean?, spark plugs need to be changed. I'm really at a loss and the only thing that I've recently done is order new spark plugs to switch out. I'm going to change the plugs this week and see if that helps but any suggestions on where to start would really help me out. I've gotten to the point where I just wanna ride the damn thing. Can anyone please help?
So last night I just cleaned out the carbs yet again. This time I ensured they were spotless. Double checked the slow jet and actually ran a wire through it this time to ensure the passageways were all clear. All the jets are stock 35 for the slow/pilot and 105 for the mains. I put it all back together and as I was doing so saw the air mixture screws. They were a little off so I screwed them all the way in then out 1 3/4 turns as per the manual. I'm going to follow up and run a test on them possibly tonight or later this week. I also purchased brand new NGK D8EA spark plugs since the old ones are fouled up. We'll see if that fixes it.
Well, After I cleaned up the carbs a bit and messed with the idle mixture screws it all idle'd well. If anyone else has this problem I only have one word: Research, Research, Research!
Yup. Doing that this weekend. Bought this giant pice of $%it! Motion Pro Tuner that drained one capsule of blue liquid already due to the high vacuum/erratic idling. I'm thinking I can still sync up the carbs with just the 3 tubes left.
Ha! I would but I have some bad news...now the bike doesn't start whatsoever. It all started with the oil pan drain plug. I applied too much pressure and stripped the threads. I ended up tapping it to a larger size (1/2 bolt) and all was well...or so I thought. I filled it with oil and started it back up. The oil pressure was a bit off (15-35 psi) but I ran it anyway. Checked the dip stick and it was at a proper level. It was still idling a little too low so I decided to mess with the idle screws again. Had the bike running for about 10-15 minutes and I noticed the oil pressure slowly dipping down. I ignored it and kept messing with the idle screws as I thought I was getting closer. Then it started radiating heat pretty noticeable. The oil pressure was now about 5 below psi and the engine shut down. I once again checked the dip stick and it was at a nice level. I was exhausted from working on this thing several hours and it was getting dark so I decided to leave it for the next day. I try and start it this morning and nothing. I ensured that the choke was up, ensured that there was fuel getting to the carbs and nothing. I ended up spraying some starter fluid into the carbs and it coughed a bit but still nothing. I went to Pep-Boys bought new spark plugs and I'm still getting the same story. Doesn't even start up at all. I ended up draining the battery from using the electric starter so much but luckily I had a spare one charging up. I pulled the brand spanking new plugs out to test the spark against the head. I get spark from cylinder 1, go to test cylinder 2 and nothing. The Clymer manual said to pull the plug cap and test the high tension lead against the head, so I did. Cylinder 2 still has no spark. My next move is to move to the Coil connections. I noticed one of the wires to the coils was a little loose (Blue wire). I unplug it and plug it back in ensuring that it has a tight fit. I also check the points and noticed that the points were touching...there wasn't any room for the feeler gauge to go through. So I adjust the points to about 0.012-0.016 in. That's when I noticed one of the points is slightly damaged. I take note of that and close it all back up. I try to check cylinder 2 for spark again by placing the high tension lead (without the cap) on the head and I finally get spark, although it's VERY weak. I put the cap back on, put the spark plugs back in and seal everything back up to get ready for another round of testing. This time it starts to cough a bit more but still nothing.
So now I'm ordering The "Real Deal" Dyna Ignition Coils, new spark plug wire sets, and new ignition points from DCC. I'm hoping I'm going down the right path but I guess we'll see...Any of you more experienced wrenchers out there care to comment?
start throwing parts at it and you'll go broke real soon
reset the carbs to stock settings and try again, you mentioned turning the idle screws all funky as it was running before it quit and didn't start again...
start throwing parts at it and you'll go broke real soon
reset the carbs to stock settings and try again, you mentioned turning the idle screws all funky as it was running before it quit and didn't start again...
I recently found a Collar O-Ring from my oil pump in my oil filter....I guess I must've missed this part when I put it back together. This could be another reason why I'm having trouble....I hope it's not a big issue.
This is the part: http://www.cmsnl.com/honda-cb750f-750-super-sport-1978-usa_model7240/collar-o-ring_15155300000/
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