HARD TO START

[billod2GPEK]

81 CB 750 C. VERY HARD TO START BUT AFTER IT WARM UP SEEMS TO RUN FINE WILL RUN LIKE A BANDIT TILL IT HITS 7500 RPM THEN STARTS BREAKING UP WONT GO TO REDLINE IN ANY GEAR SEEMS TO RUN PAST 7500 A LITTLE IF I ROLL ON A LITTLE EASY. HAD CARBS APART 2 TIMES EVERY THING LOOKS FINE AND THEY ARE SUPER CLEAN. NEW PETCOCK AND LINED TANK. SURE WOULD LIKE SOME HELP. THANK YOU.

[80 bobber]

could be a timing issue, also did you sync the carbs?

[billod2GPEK]

only bench sync but this week when i get the tool i will sync what kind of timeing issu ? thank you

[billod2GPEK]

[woodsrider250]

Adjust valves to .005-.007

Vaccuum operated safety petcock can be removed, and just use the manual one...This POS makes them hard to start, especially if they've sat for a while.  

Next time you have carbs apart install #72 primary main jets, the #68 is too lean in most places (EPA leaned out during this era).

[billod2GPEK]

put new man pet cock in done away with vac. petcock cleand and lined tank

[mikey440]

 syncing the carbs is for idle only, also if your crapping out at 7500 that probably means your main jet is too small, primary jet is for mid range and main will be working at 7500 rpm,s,,,perhaps you dont have the carbs clean enough,,hope this helps,,mykey440  also your hard starting issues might be related to clogged idle jet circuit, suggest cleaning carbs again , install inline fuel filter or 2...

[mikey440]

 if theres any crap left in that tank and you dont have inline fuel filter you will be taking those carbs apart time after time,,,honest

[billod2GPEK]

thanks mikey                                                                                                                                              them carbs are super clean may need bigger jets. its actually a 1980 eng. i put in a 1981 frame. them carb are a real bear getting on & off. i thought sync was only fof idle but every one said sync so i fig i must be missing something. just rejeted my buddys v 45 now them carbs were the worst to get back on. thanks again.    what size jets would you suggest?            

[vern401]

hard starting can be a mix of things. like everyone is saying make shure your carbs are clean. try a different fuel tank "I use an old plastic lawn mower tank" that gravidy feeds the carbs. you would need one to sync the carbs anyway. Make sure all the plusg are good too. the timing thing that was refered to may be the timing advance. they tend to rust up on older bikes my sl350 had that problem. make sure your pilot jets are set right too. your fuel level in the floats is also very important not enough in them and it starves the engine to much and it floods.

[vern401]

Sync affects both idle and high speed. what your doing is equalising the vacuume between all the carbs.

[billod2GPEK]

thanks guess ill sync them this week pulled carbs after 5000 miles not a bit of crap in the bowls

[billod2GPEK]

thanks guess ill sync them this week pulled carbs after 5000 miles not a bit of crap in the bowls

[vern401]

make sure the float height is right and the pilot setting is right. My 750 is real picky about the float height. It also is a bear to start is the battery is even a little low.

[mikey440]

my jets are stock, 68 primary and 102 main, i have no problem pulling power all the way to red line,
 my idle fuel mixture screws are turned out 2 !/2 from lightly seated, dont turn them too tight when adjusting they will break, then your you know what!!  yes make sure you have good battery, fresh plugs,,
 do you have stock airbox, if you dont get one,,throw those pods away, these carbs work on vacuum and if you have individual air filters on every carb its a pain to get too run right, check petcock for good fuel out, put in an inline filter to catch the crap,,also if its a hard starter perhaps your choke is not workin good..ok good luck, let me know, mikey440

[Re-run]

+1 on what mikey said.
I would add that you should check your plug color. Get some fresh ones and put them in. Get the bike out on the road and run it hard through the gears, when it tops out in 5th, pull the clutch and hit the kill switch at the same time. Keep the clutch pulled and brake to a stop. Pull the plugs out and see what color they are.
Only other thing is check timing, maybe that was already suggested though.

[billod2GPEK]

took bike up in the mountains today and really floged it hard seems to be running up to redline now put in new gas ran it really hard for 250 miles runs better thanks for all the tips ever one

[vern401]

If i'm correct you bike has the CV carbs on it. If it does make sure the slides that move the needle inside the carbs all move freely. My CX 500C was acting simelar to your Discription and one of the slides was hanging up on it. Do a real thurough cleaning of the carbs ensure ALL ports and jets are clean. Check the spark on your plugs you should have a nice strong spark if you find 1 or 2 are weak it may be a coil or points or condensor problem. Syncing the carbs does help the idle allot but out of sync carbs will no accelerate properly as on carb is trying to feed faster than the others. Make sure your floats are set correctly to little or to much fuel in the bowls will effect how the bike starts and runs. If you have a compression tester what is the compression of your cylendars? If I think of anything else I'll let you know so you can be back to enjoying your bike not fighting to start it.