Question about Honda CBX 750 F Motorcycles

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I have a 78 honda it has been sitting, won't idle

I have a 1978 honda 750 four,it has been sitting a while put in new battery , took carbs off cleaned them, it will start and run on full choke, will not idle? , fresh fuel, fresh oil, mixture screw(s) all four, seated ;backed off two full turns. wont idle after its warm either.where can it **** air from-to need so much fuel?rubber tubes from air filter intacked and the ones to the heads are ok

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The stock pilot screw setting is one and one half turns. The usual problem for not idling is that the slow speed circuits in the carbs are still plugged up. Secondary cause is usually that the carbs are not in sync > The carb slides don't all move upward at exactly the same moment. If you haven't installed new spark plugs, do it. Soak the carbs in denatured alcohol after removing the slides and float bowls. Finish with spray carb cleaner and compressed air. Spray into all the drill holes, ( circuits ), in each carb. Install an in-line fuel filter to prevent trash from the gas tank getting into the carbs.

Posted on Jul 04, 2010

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2 Answers

Where should I start on a motorcycle that has been sitting for 20 years?


Hi Nick:
What a great project.
- I'd start with a really thorough clean up.
- You've mentioned the gas. Definitely, drain the tank, hoses, carbs, and clean the carbs. If there's a filter I'd change it.
I wouldn't even try to run it without cleaning the carbs first.
- Replace the battery, oil, and spark plug.
- Engine coolant?
- Tires? I wouldn't worry until I had it running but definitely replace.
Patience & time. You'll have an excellent bike.

Jul 13, 2015 | Honda Motorcycles

1 Answer

I have a 1978 gs 750. I have had the bike for three weeks now. Put new coils , cleaned the carbs (new gaskets) I have taken apart the carbs 5 times now. Had it running for a bit but would bog out pretty...


Could be a number of reasons
1-your main jets are too big
2-float level to high
3-blocked exhaust
4-points or CDI(please confirm)
5-carb manifold rubbers leaking

Please get back especially No4*

Jul 06, 2011 | 1978 Suzuki GS 750 E

1 Answer

Just bought a 1993 suzuki gsxr 750. has been sitting in a garage for 2 years. we took the carbs off and cleaned them really well, changed the oil, and air filter and we added new gas. bike starts up and...


If is runs better with full choke, then the bike is lean, check for air leaks at the carb manifold, vacumn cracked hoses, non standard exhausts, perhaps the mufflers have rusted out while sitting

Apr 24, 2011 | 1993 Suzuki GSX-R 750 WP

1 Answer

2201 honda shadow ace 750. bike has been sitting over a year. replaced plugs, battery, got started but barely idles at full choke. A little throttle or push choke at all and it stalls. Tried Sea Foam...


You are correct about carb dissembling & cleaning bare min drop bowels & carb clean the jets idle & main any adj screws remove & spray out passages. count the turns so to replace screws to same place.. biker bandit may have some dias...

Apr 08, 2011 | 2001 Honda VT 750 CD Shadow A.C.E. Deluxe

1 Answer

My 1982 Honda v45 will not run without the choke on. It sat in the garage for years with old fuel in the tank. We drained the fuel, changed all the oils, etc and completely REBUILT all 4 carburetors. I...


The slow jets and adjoining passageways are still dirty. As painful as it may be , take the carbs off and clean the slow circuit again or it will never idle. Double check the fuel pump is working properly and the fuel filter is not plugged. One time it took me four cleanings to get all four carbs working on a Suzuki that sat for five years. Also make sure none of the carburetor boots have developed rips from age.

Aug 31, 2010 | 1982 Honda VF 750 S

1 Answer

Engine will not start,almost sounds like it is backfireing out of the carburater ,I cleaned out the old gass and put new in, cleaned gas lines,blew out carb with air two times, it ran for about 10 seconds...


Pour a large amount of carb cleaner into the gas tank
With choke on full, pull cord often to work carb cleaner into carb and then let it sit for a day or four.
Your carb is dirty for sure.
The venturi and jets are so small on these carbs that they are easily clogged with gunk from old gas

Aug 05, 2010 | Honda Pressure Washer PSI 3000

1 Answer

My 1993 Honda Knighthawk wont run.


The slow circuit of your carbs are dirty. you need to remove the carbs from the bike and thoroughly clean the internal passageways and jets. that should solve the problem. Always drain your carbs for storage and use fresh gas when you start up after long storage.

May 15, 2010 | 1993 Honda CB 750 Nighthawk

2 Answers

Starts fine but will accelerate only with choke


stabil gums up carbs drasin the gas and run a carb cleaner through that should fix the problem

Mar 09, 2010 | 2005 Honda CB 750

1 Answer

I have to have full choke when I start bike, warm or cold.I've cleaned carb,s and passages seem clear. I,ve been running bike with air cleaner off, will that make a differance? GS 750 - 1978


your engine will **** in an average of almost a teaspoon of dust an hour of running without a airfilter on. this dust wears out the rings in your engine and everything else it touches in your engine. Lower compression and partially clogged jets lower the vaccum that your carbs pull in. Your bike should have a vaccum operated petcock that allows the fuel into your carbs. My guess is that you have low vaccum pressure. You might just need to replace a vaccum line or a petcock. Try pulling off the vaccum line from the front of the second carb and sucking on it until you see the fuel line fill up a little (don't worry, gas doesn't go threw the vaccum line so you won't get a mouth full of gas). Once you see the line about half full of gas or better. Try starting it up without the choke (engine should already be warm). The reason why I think this might be the problem is because when you choke a engine on these carbs, you increase the vaccum in the lines. Let me know if when it is warm, before you start it, if it already has about half of the gas line filled up. Good luck and let me know how it works out.

Sep 13, 2009 | 1978 Suzuki GS 750 E

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