Topic: Bike wont start 77 750

[Sd455]

I cleaned the carbs (disassembled, cleaned reassembled). The bike started after many cranks and direct priming (shot of fuel through the spark plug hole). It ran rough and not responsive, but it got up to temperature. That's the only way it will start. Bowls have fuel in them but the engine seems starved. Getting good spark. Everything looks good around the points. Everything is factory set, except the carbs. Any ideas?

[Johnie]

Did you put all the parts for each carb back into the carb it came from?  Did you check the float height?  Did you check the air screw settings?  Did you sync?

[robermcm]

I'd think about how I cleaned the carbs too.  You soak or just spray with carb cleaner?  Some emulsion tubes don't clean up well without disassembly and soaking. Your slow speed circuit could be gummed up worse than when you disassembled.

[mj_honda]

I'd think about how I cleaned the carbs too.  You soak or just spray with carb cleaner?  Some emulsion tubes don't clean up well without disassembly and soaking. Your slow speed circuit could be gummed up worse than when you disassembled.

+1 on the slow jets and float height. The manuals will say they are not removable but they are. They pull out straight. Just use something to wrap around them and pull out. Don't wiggle back and forth.

If you did a bench sync, an actual sync with gauges won't do you much good if it is still not running pretty good to begin with. The bike should already be running in decent order before doing a sync with gauges.

Did you check the rubber bits (fuel lines) between the carbs? These can be blocked which will cause it not to run correctly. How do the header pipes feel with a quick touch? Are all 4 the same temp?

[Sd455]

I soaked them in Chemtool then I sprayed through all the passages with carb cleaner, then blew them out with compressed air. Removed pressed in jet, cleaned that too. Put all parts back to original carbs. I eyeballed the floats, don't think I changed the settings (which where last set at the factory) when I removed them. Backed out the air mix screw 1-1/2 turns. Got a Carbtune to sync them but I cant get it to run. All fuel rails are clean.

All 4 pipes seemed to be the same temp.

Should I pull them off again or can I check something while they're on the bike with the bowls removed?

[BobbyR]

I would say you did not rod out the slow jets with a strand of wire. There are deposits from some of the gas additives that carb cleaner will not dissolve. A strand of lampcord wire will break them up and the carb spray will wash away the loose debris. Rod out all of the passages. Your 77 and my 78 have accel pumps, that is an area that should also be checked for general drivability. I would first check to be sure your choke butterflys are closing before you remove the carbs.

[Sd455]

I very carefully cleaned out the slowjets (I could see light through them after I was done), after soaking, with guitar string. Accel pump is clean and choke butterflies are functioning properly. Could I be missing something simple?

[speedy gonzalais]

how does it run once its warmed up ?

[Sd455]

I really only got it to start once, I don't want to kill the starter. It couldn't hold an idle and only when it got real warm did it respond to the throttle.

[BobbyR]

That fact that you needed to prime to get it started speaks to fuel not getting uo to the air horns from the float bowl. If the 77 is the same as a 78 those are not air screws, they are mixture screws. Try turning them out a few turns and see if that helps. 

[Sd455]

Thanks.They are mixture screws. I'll try playing with them tommorrow.

[Triffecpa]

Had the same issues with a 78F.  Turned out to be float height settings.  Got those sorted and it starts at the first push of the button now.

TR

[Sd455]

Got it started, cant get it to idle. Floats seem to be set properly.

The only thing I could think of is that the slow jets are still dirty so I took the bowls off took the jets out, everything seems clean.

Sprayed carb cleaner through every hole I could find,everything is flowing.

Does anyone know if these slow jets (pressed in jets) are available?

Also, does the air box need to be on for syncing?

[Honda_Nut]

Clean holes in the emulsion tube (crosswise in the main jet)?

[speedy gonzalais]

I think you can rule out the sync for now that wouldnt stop the bike from starting and as far as i know the idle curcuit wouldnt affect the way the bike runs at high rpm and my 650 run with totaly blocked idle jets and it started on the button, Is the bike newly aquired did it run ok before rebuilding the carbs?

[Sd455]

Yes its newly acquired. The prior owner (original) said it ran fine ,I know him personaly. It only has 2200 original miles on it. It sat since 1981.

[speedy gonzalais]

if you have cleaned the carbs then its gotta be somthing else, Try putting your hand over the back of all the carbs and crank the engine, that should suck air thru the float bowls priming the engine, if she dont start after that id think about checking a few other things like the valves, As its been sitting so long the valves probably wont seal that well anymore or some or even all of them will prob stick, If you can get it to run long enough for the engine to get hot then they will stop sticking eventualy, and back to the valve leaks if they are theres only 2 ways to get them to seal, either head removal wich in all honesty u dont want to do, or get the bike warm and run it rich if you can keep it running long enough the rich mixture should build up lots of carbon on the valves helping them seal, and change the plugs if its been sitting since 82' there be knackard.

[Sd455]

dids, I got it to run by putting my hand over the carbs. It will run as long as I keep it over 1500 RPM. Below that it gets rough and stalls. While its running it occasionally pops. Pipe #3 is getting very blue, Pipes 1 & 4 are getting a little less blue and #2 is getting a little golden. Obviously running at different temps. I have the mixture screws set at around 1-3/4. Any ideas?

[Tower]

If it runs when choked, but roughly and seems to be starved of fuel, it actually sounds like air leaking in behind the carbs.  Ensuring the engine-side boots are on correctly and soundly tightening the clamps should fix that.  Also, the rubber may be cracked and letting in air, in which case new rubber is required.  If no leaks then a few sprays around the boots with "Quick Start" starting fluid, should produce no change in the engine speed.

Could also be air getting in around the exhaust port (i.e. loose header or over-crushed gasket), although that's doubtful, as that would show up as one pipe hotter than the others.

Edit: An airbox is slightly restrictive, so running without one is like leaning out the mixture, in this case making the situation worse.

[WFO]

Probably a dumb question but is the tank clean and putting out a good flow?? ( air vent maybe)? ( (clogged screen)??

[speedy gonzalais]

Checkin the boots is a really good idea il go with that and checking the tank too, Where the carbs covered in varnish inside? the idle jets block easily it will only take a bit of crap in the tank or some still in the carbs to block them up, I cleaned mine twice on the 650 before i was happy, Old fuel goes like cyrup if there was any left in the bike then clean the tank, I used paint thiners in mine it desolves that slime in no time and soak the carbs jets every thing in thiners over night then give them a good blast with air, while there off check them boots for cracks, I found a good tempory fix for mine was electrical tape wrapped round them and a bit of plumbing tape inside, worked great till the new ones arrived.

It would be nice to see a few pics if you got any

cheers dids 

[Sd455]

Putting the airbox on seems to have fixed everything. After it gets to temp (takes a long time to warm up)it idles real nice at around 1000 RPM. The valves sound a little sloppy. Do they typically make noise?

Took it for a ride, engine is great but the breaks froze up. I didn't clean the calipers, so back to the brakes. Any pitfalls here?

I'll send pics when its all back together.

PS the carbtune sychronizer is excellent.

[BobbyR]

That is what it takes to get these old girls running. Point by point restoration. Once you have everything done, your tinkering time drops down to normal maintenance.

[Sd455]

Well, finally got it right. Rides great stops great. Now what?

[BobbyR]

Well, finally got it right. Rides great stops great. Now what?

Now you ride it like you stole it and reward yourself for all the work you did.