Topic: overhauled carbs now wont run at all

[Buffo]

1978 cb750k8

Rebuilt carbs
did the one and a half turns of the pilot screws

Does nothing. not even spit and sputter. nothing

Help


don

[Bob Wessner]

Hope these don't sound like a dumb questions, but have you verified that you are getting fuel to the carbs (i.e., slightly unscrew drain screws and confirm there is fuel in the bowls). Did you check/set float height? Are you sure there are no fuel flow issues from the tank/petcock? Are all the plugs firing?

[DammitDan]

Don't know if this is the case with a 750, but when I tried to restart my '82 650 after the carbs had been dry for some time, it had the same conditions...  cranking the engine with not a hint of firing.  I sat down, thought about it, and searched through the sohc4 archives, and found out that I had to inject a little fuel into the bowls as a sort of "starter fluid" before it would catch.  Did that, and it fired right up!  Happiest day of my motorcycling career, until it siezed 15 minutes later.  But that's another story 

Of course, the 650 has a vacuum line running from the tank, so once again it may be a different situation.

Also, make sure all your spark plugs are firing correctly.  There should be a guide somewhere on this forum if you search for it 

[mikeb4]

I think Bob & Dan are right on the fuel into the carbs.  When I did my 1977 750F carbs last week it took a long time for the carbs to fill with fuel.  I cracked the lines on each bowl to make sure they all had fuel before I really cranked on it and even used a rubber hose with a towel wrapped around it on the filler hole to blow some pressure into the tank to speed things up. 

[eldar]

Well as long as you have a clean petcock and filter and your fuel lines are not clogged or blocked in some way, you should get fuel in the bowls.

You never mentioned how the bike ran before you did this. OR what all you actually did to the carbs. You may have thought you cleaned them and actually made it worse. Does happen.

[Bob Wessner]

...and actually made it worse.

Ha, I've done that more than once. 

[eldar]

Yes we are all aware that you are the national carb removal champ!

[Buffo]

Well... carb overhaul intailed:
1. stripping down completely and dipping in berrymans. Clean as can be. blew everything out. I am sure nothing is clogged
2. replaced : top cover gasket,jet needle and clip, pilot screw, spring, O-ring and metal gasket,main jet, needle seat, needle valve, float bowl  gasket, O-rings for fuel connector pipes, O-rings for drain screws and the screw that you sync the carbs with.

throttle slides in PERFECT shape
Plenty of fuel in float bowls
full tank of new gas
new fuel filter
fresh oil and filter
2 brand new dunlop k491 elite II
set of clubmans from carpy
loads of spark

It ran  before i did the over haul but like crap and  only while reving the throttle like mad, the carbs were filthy

Don

[Bob Wessner]

OK, you seem to have verified the basic three, air, fuel spark. You say good spark, but is it happening at the right time? What's the condition of the points, condensors and timing?

[eldar]

You dipped in berrymans but did you run anything through the jets? Nothing will clear a clogged jet like a small bit of wire or a carb cleaning tool.

Also, did you set you float height? I also noticed you did not mention that you changed the float needles. You could be WAY flooding your engine.

[Greg]

buffo
check the idle screw adjustment -- if it is all the way backed out than the bike might not run -- i had the same shivers as you when my wouldn't start fter a rebuild, then adjustd the idle screw and it fired right up!
good luck!
greg

[Bob Wessner]

You dipped in berrymans but did you run anything through the jets? Nothing will clear a clogged jet like a small bit of wire or a carb cleaning tool.

Good point. When I cleaned mine, I through everything in the cleaner (disassembled) jets and all and used canned air on everything after. However, since I was using rebuild kit I didn't pay any attention to the jets. Recently, when I thought I might go back to the stock jets, needles, etc. I examined my the old, "cleaned" idle jets to discover they were in fact, clogged. I threw them back in some Yamaha for a half hour and I had to poke a fine, soft wire through them to clear them. So far, haven't had to go so far as to reinstall them, but if I do, I know they're actually clean now.

Signed: National Carb Removal Champ. 

[Buffo]

looking around i have found 2 points of interest
point 1 is that i forgot to put in the rubber stopper in the accelerator pump assembly. which is now destroyed (the rubber stopper) and i need a new one. gas comes out of the pump when you twist the throttle.

point 2 is tht i didn not put in a plastic washer or spacer on one of the link arm assemblies. it is not totally round but has 2 flat sides and on the rounded sides it has a lip on each end, it went on the rod (throttle link set)that opens and closes all the carbs . does this spacer need to go in? The throttle seems to work smoothly enough and i dont remember what one it went to.

on to the points...they "look" Ok. I am reading my clymer manual but I have never delt with points before. I will get the dyna $ and the proper coils for it when this pile runs for a day or so but for now it needs to run. the point contacts look flat and aligned good. there is a couple spots of rust on the springs (?) With the cover off i hit the starter. Should i be able to see the points sprk or something? Mine spark nicely but not every time they go around.
The pile dosent run so i dont know how to check the timing

the main jet and needle jet are new

Don

[Bob Wessner]

What you see at the points in terms of a spark doesn't mean much. As a matter of fact, the spark there should be minimal to non-existant. That you see any at all at least indicates juice getting that far. You can set the timing without running the engine, you do it statically. Go to the FAQ's for instructions on this. If done correctly and accurately, it is a very satisfactory way to set the timing. Later, when running, you can verify with either a timing light or a dwell meter.

[eldar]

Well right there with the accel pump, that could be flooding you to the gills.

I got a pump from partsnmore.com and it seems to work just fine. it was also only about $12 I think maybe a bit more.

That spacer helps keep everything aligned and helps minimize wear. If it is the spacer I am thinking of. Install it.