Topic: 77 CB750 only runs with choke, won't take any throttle

[AndyJ]

Hi guys,

You have all been so helpful before with some of my ignition dilemmas I'm hoping someone could comment on this problem: my build is almost complete, it's a 77CB750K, purchased a few months ago and ran good. After a few months of painting and Powdercoating etc. the bike is back together and she won't run unless I'm using the choke. I have cleaned the carbs and even recleaned and found I had 2 blocked pilot jets cleaned then and its still only running with choke. With full choke she starts 1st kick every time, but then revs to over 4K rpm so I'm forced to fiddle with the choke cable to bring the revs back down. When I try to even slightly crack the throttle open she dies out.
Any help is greatly appreciated.
By the way my set up is as follows:
Carpy 4 into 1, pod filters, new plugs, wires , caps points condensers etc.
77 carburetors with accelerator pump, cleaned.
120 main jets and 35 pilots jets, not sure on needle setting.

Thank you,
Andy

[Rgconner]

Verify that the choke is operating as you expect it to operate.

In the ON position, the butterflies should be vertical, in the OFF they should be horizontal.

Quite frankly, the problem you describe indicates you have it in ON when you think it is OFF.

[TwoTired]

Verify that the choke is operating as you expect it to operate.
Quite frankly, the problem you describe indicates you have it in ON when you think it is OFF.

Good to verify choke plate full closure.  But, it very difficult (perhaps impossible) to get the PD carb's knob and cable choke system to work backwards.  Particularly as it is coupled with the fast idle cam.

For Andy:
Still sounds like there is blockage in the pilot jet system and that your accelerator pump system is weak or inactive. In addition to the issues you've added with the pod filters (reduces all carb jet delivery volumes).
Then there is "cleaned" and there is "proven clean".

Have you cleaned the I.M.S (Idle Mixture Screw) and the hole it blocks when "closed"  Have you over tightened the I.M.S?  And what setting have you applied?

Cheers,

[madmtnmotors]

Don't forget to check the fuel flow from the tank itself. These have a filter screen inside the tank that shrouds the overflow tube. Disconnect the fuel line at the valve, connect a seperate line to the fuel valve and check the flow of fuel into a suitable container.

[AndyJ]

Thank you for the replies thus far, I have confirmed that the choke is operating correctly with the butterflies closed when starting.
The IMS are clean an I've cleaned the holes the screw into. I have them set at the standard 1.5 turns out which after reading other posts probably need to be greater.
I have pulled the carbs back off and found that the accelerator pump was blocked. I've removed the and cleaned the nylon retainer, ball and spring in the Mickey ears and confirmed the correct airflow. But now I've found that the passages to all four carbs from the accelerator pump are clogged. I have sprayed come carb/choke cleaner and gotten it to come through #3 and barely out of #4, still can't get anything out of #1 or #2.
Any advice on getting those unclogged would be great.

Thanks again!
Andy

[Rgconner]

Verify that the choke is operating as you expect it to operate.
Quite frankly, the problem you describe indicates you have it in ON when you think it is OFF.

Good to verify choke plate full closure.  But, it very difficult (perhaps impossible) to get the PD carb's knob and cable choke system to work backwards.  Particularly as it is coupled with the fast idle cam.

I was more suggesting that Andy may have been operating the choke backwards. I suppose that is easier on my bike as it is a lever and is 90 degrees off what the butterfly is set at.

[TwoTired]

Yes, the early 550s are the same way and some operate them backwards at first.  But, the choke knob and cable employed on the PD carbs are far more intuitive in that regard.

Cheers,

[Spanner 1]

Usually the tiny squirt nozzle gets blocked on the squirt post if no squirt.... you can poke a very small wire in the hole ( I used an 'E' guitar string) Have to poke from the motor side of the posts ( obviously  ), so carbs need to be off the bike. You can fill the pump 'sump' and check operation on the bench tho' before putting the carbs back on the bike.... good luck.

[lucky]

Idle jets clogged.
Also on the 1977 do not forget that the accelerator pump and nozzles must be working.

[grcamna2]

Usually the tiny squirt nozzle gets blocked on the squirt post if no squirt.... you can poke a very small wire in the hole ( I used an 'E' guitar string) Have to poke from the motor side of the posts ( obviously  ), so carbs need to be off the bike. You can fill the pump 'sump' and check operation on the bench tho' before putting the carbs back on the bike.... good luck.

I like that way of cleaning them out and I've sprayed them out individually with a can of Gumout...but never tried trying to push a very fine wire into them...I wonder if after that I can try spraying those little posts out the opposite way w/ Gumout after trying the wire trick,kind of back flush them.They sure have seemed to be a bear to clean out and next time I have a set to clean I'm going with this method.
The bike really won't run cleanly with out those little ports being 100% clean,will they ?!

[bollingball]

http://forums.sohc4.net/index.php?topic=91557.0

AndyJ check this out saw it and thought it was a good little trick.

                                               Ken

[AndyJ]

Thanks for That link Ken. I finally got all four of the little sprayers to spray. Did the cleaning on the pump ball after determining that it was stuck.
I have set the float levels to 12.5 mm IMS are at 2.5 turns out, fresh gas.
Starts first kick with the choke closed and it still revved to all he@%....??
I was able to open the choke after a few minutes and it would idle rough but not take any throttle. If I wacked it she would suck wind and die, if I ever so smoothly and slowly open the throttle she would roughly build rpms. But I am hearing a spitting sound coming from the pods..?? What could this mean?
When I rode the bike home it had this same set up and ran great, could changing the points screw up the timing? Could my timing be off?

I'm beginning to feel at a loss. Thanks for any help or thoughts on this.

Andy

[Rgconner]

Spitting carbs is timing and/or too tight of valves clearance I think...

Won't hurt to check those, got to do it anyway.

Oh, good trick with these: hook the timing light up to a different battery. Strobe will fire more regularly and the mark won't jump around.

If you get it timed right and it is still rough, you could try advancing it a bit, see if it helps.

[Bob3050]

I would check for vacuum leaks at the intake manifolds by spaying wd40 (or something like it) on the manifolds while the engine is running. If there is a leak you will hear an rpm change and possibly smoke from the exhaust when you spray into the leak.
Bob

[AndyJ]

I will certainly check both of these. I noticed that the valves are very noisy. I pulled the points cover and saw a couple of good arcs while getting it started.

I did manage to get around the block pretty much idling, it still wouldn't take any throttle but when I closed the choke full and revved it she took off with throttle cranked open.

Thanks for the comments so far keep the input coming.
Regards
Andy

[madmtnmotors]

could changing the points screw up the timing? Could my timing be off?

Yes.

[bollingball]

You did say it ran great when you brought it home with the same set up. Then you changed the points this is the first place I would look. As a matter of fact I would go over the whole 3K tune up. If it was running great why did you mess with it? I guess it was time for the tune up.It may not be but I think you got the points or timing off or both. What else did you change. You know now you can not change the points ONLY. Running great with pods some say it can be done but I doubt it does through the entire power band. You will see when you put some more miles on it.
 One more thing Did you (pull out) the The slow jets? This (MUST) be done it is the one thing I did not do the first time because the Honda factory service manual say they don't come out. Then after finding this site I found out they do. Also the fast idle cam (Must) be set up correctly for easy cold starts by that I don't mean cold outside I mean bike has not been started for a few hours.


                                                  Ken

[AndyJ]

Hi Ken,
It did run good when I brought it home, but I was doing a complete cosmetic rebuild (cafe build) since it ran good I didn't want to get into the engine. It did however have a cracked header which resulted in an exhaust leak on cylinder #4.
I had purchased a new Carpy 4 into 1 system to replace to old rotted 4 into 2.
When I put the bike back together it was hard to start an ran very rough. After a lot of reading on these forums and a lot $ later, I started replacing parts hoping that would fix the problem. Since then I have purchase and installed new points, condensers, plugs, caps, coils, starter solenoid, pods the old ones were shot, and get this....new carburetors (I damage the original set by soaking them too long).
The new carbs have been cleaned three times, the idle/ pilot jets were indeed clogged, and the accelerator pump and nozzles were not functioning. I disassembled the pump and removed the little ball cleaned it all up and finally got all four nozzles to spray. I thought I had everything ready to go, when I put the carbs back on its pretty much doing the same thing as when the jets were clogged and the nozzles weren't spraying. Maybe they're clogged again?? The timing may also be off due to some spitting, it was also spitting with the original carbs on..
I'm going to attempt to adjust the valves and do the timing neither of which I have bet performed. I need to get some feeler gauges and already have a timing light. Hopefully my searching here will get me through the process of both.
Thanks again for all your help.
Andy

Please excuse any typos I'm responding quickly from my iPhone

[madmtnmotors]

It did run good when I brought it home, but ....
I had purchased a new Carpy 4 into 1 system to replace to old rotted 4 into 2.
When I put the bike back together it was hard to start an ran very rough.

new points, condensers, plugs, caps, coils, starter solenoid, pods the old ones were shot,
and get this....new carburetors (I damage the original set by soaking them too long).

The new carbs have been cleaned three times, the idle/ pilot jets were indeed clogged, and the accelerator pump and nozzles were not functioning. I disassembled the pump and removed the little ball cleaned it all up and finally got all four nozzles to spray. I thought I had everything ready to go, when I put the carbs back on its pretty much doing the same thing as when the jets were clogged and the nozzles weren't spraying. Maybe they're clogged again?? The timing may also be off due to some spitting, it was also spitting with the original carbs on..

I'm going to attempt to adjust the valves and do the timing neither of which I have bet performed. I need to get some feeler gauges and already have a timing light. Hopefully my searching here will get me through the process of both.

WOW!  Talk about your variables...

Follow Ken's advice and complete the 3K tune-up, which includes timing and valve lash. You are going to have to work through a process of elimination to find out what it's NOT. Get the timing and valves set in order to rule those items out, check for spark on ALL cylinders, before you get back into the carbs. 

Keep us posted...

[AndyJ]

Quick update:
Points gap was way off. They are now set to .014.
Started first kick today and I noticed the 2&3 points arcing all over the place, arcs were jumping from the spring/points to the plate.
Any idea what could cause this erratic arc?
Thanks fellas.
Andy

[Danno]

two things your condensers are shot and the screw that conducts to the spring may be loose