Author Topic: A little help.... (Read 2450 times)

SurfinBird · « **on:** July 05, 2011, 09:32:27 AM »

I got my '78 CXB750F running and took it for a road test and had a few things go wrong.

It was fine for about a block, running a bit rough, one of the valves needed to be adjusted and I haven't synced the carbs or set timing. I was getting a bit of popping and then it bogged and shut down. I was able to get it started and got it about quarter the way home and it bogged and stopped again. A bit of pushing and trying again and i got it rolling, but real slow. I opened up the throttle and only got it to about 20mph in 1st and it shut down again. I let it rest about 15 minutes and it started up and I got it home. Home here are a few more details.

- All pipes were hot so I think they were all firing
- Wouldn't get past about 5000rpm
- Wouldn't idle, but after a rest and restart it would
- Didn't lose any lights when it died
- Noticed a tappet cover was loose, oil was coming out, not much.
- Putting it gear was a bit rough, but it didn't pop out of gear or not go into gear at all
- How can I tell if the oil is flowing?
- RPM's felt like it hit a flat spot it acceleration then drop off and shut down

Any thoughts?

SurfinBird · « **Reply #1 on:** July 05, 2011, 09:33:04 AM »

Sorry, CB750F, the X decided to make a guest appearance

ekpent · « **Reply #2 on:** July 05, 2011, 10:33:45 AM »

Wonder if all the carbs are getting gas ?? Sounds like it may not be.

BeSeeingYou · « **Reply #3 on:** July 05, 2011, 10:45:55 AM »

Quote from: ekpent on July 05, 2011, 10:33:45 AM

Wonder if all the carbs are getting gas ?? Sounds like it may not be.

That's where I would start. Sounds like a restricted fuel flow. Stuck float, plugged needle valve, clogged filter, dirty tank, old gas? A little more info on what you have done to the bike.

DJ_AX · « **Reply #4 on:** July 05, 2011, 11:08:00 AM »

Quote from: SurfinBird on July 05, 2011, 09:33:04 AM

Sorry, CB750F, the X decided to make a guest appearance

That B!TCH .. I hate it when that happens!

SurfinBird · « **Reply #5 on:** July 05, 2011, 11:15:04 AM »

It wasn't running when I bought it so here's all I've done to get it to where it is:

Replaced clutch cable

De-rusted the tank using prep n etch. New petcock (no new inline filter, but see fuel flowing through it)

I've cleaned the carbs (adjusted the floats, cleaned the jets w/ guitar wire. Only pulled 1 slow jet to swap out a new #4 body), replaced the accel pump, the needles looked good and moved with the trottle control. All the bowls are getting fuel with no overflow.

Replace plugs on all 4 plugs, getting spark on all of them.

Adjusted the valves.

Gas might be a month old.

I was running it without the airbox, but didn't take it farther than around the block and it was idling ok. Wouldn't idle with the choke all the way open.

I haven't synced the carbs and one of the valves need to be adjusted. Looks like another carb cleaning?

DJ- if the real X showed up I would have found a way to get that thing running....

DJ_AX · « **Reply #6 on:** July 05, 2011, 11:20:54 AM »

Ha ha .....

I would strongly strongly recommend an inline fuel filter!
I had to clean my carbs a few times before I got one... and the point.
It doesn't take much to clog these carbs.

Also ... as much as the system is affected by air/fuel balance .. I'm surprised it ran at all without the airbox. You really need all the components in place before you can know what issues you may have with it.

BeSeeingYou · « **Reply #7 on:** July 05, 2011, 11:52:17 AM »

I am still going with the restricted fuel flow. It may flow enough at idle or low rpm but when you run the bike it won't keep up thus you get a little way down the road and it dies. Let it sit and the bowls fill up and you get a little further. It will also run lean without the airbox and as the bowls drain even more thus the popping. Either replace the inline filter or get the proper petcock filter and get rid of the inline filter completely (my recommendation). It's not clear if you removed and cleaned the idle jets or just the one but they all should be checked. How is the airfilter? Don't run it long or far without the airbox as it will run lean and hot. Lucky you have an F as the airbox is easy to take on and off.

SurfinBird · « **Reply #8 on:** July 05, 2011, 01:01:15 PM »

I'll try taking the online filter out of the picture. The petcock is for a '77, I think, I couldn't find the exact one for the '78. I only cleaned the one slow jet, they are pressed in and didn't want to pull them if I didn't have to...after pulling the one I knew I should have pulled them all. Showed me didn't it? I ordered a new air filter, should have it tomorrow.

I'm getting less worried, a fuel problem sounds like the culprit.

madmtnmotors · « **Reply #9 on:** July 05, 2011, 04:44:52 PM »

She's starving for fuel, my money is on the in-tank filter screen.

SurfinBird · « **Reply #10 on:** July 05, 2011, 05:09:25 PM »

The petcock is for a 69-76 CB750F, it came with a screen that fits over the stem, but, that doesn't fit into the tank. I figured the in line filter would do the job. Could this be the problem?

BeSeeingYou · « **Reply #11 on:** July 05, 2011, 05:35:15 PM »

That looks like the 77/8 K petcock. Close but I think the fuel outlet should point out the backside and not to the side. The 77/8 F petcock is the same and not available but I think the filter is the same for the K and F. I would think it would fit. Did you put a liner in your tank and it needs to be scraped out of the bunghole.

camelman · « **Reply #12 on:** July 05, 2011, 05:47:25 PM »

Check your timing and the advance unit too.

madmtnmotors · « **Reply #13 on:** July 05, 2011, 05:49:47 PM »

The 77' petcock points towards the rear, the 78 petcock points to the engine. The in-tank screen is a bear to remove without damaging it (it's been there for 30+ years) so you need to look and see if the old one is still in there. Slide a small screwdriver in between the plastic and the fuel bung until you can grab it with needlenose pliers and twist/pull the old one out. It would make it impossible to install a new one if the old one is still in there.

The picture is definitely a 77' petcock, earlier F's and some A's may have used the same one. The 69-76 is vastly different.

SurfinBird · « **Reply #14 on:** July 05, 2011, 05:56:03 PM »

When I de-rusted the tank I didn't see one, but the collar may still be there. I'll check. Would that make it so I wouldn't need an inline filter?

cookindaddy · « **Reply #15 on:** July 05, 2011, 06:03:14 PM »

The in tank fuel filter from Honda is GREAT. If you can install a fresh one without your tank coating being in the way, it will serve you well, much better than an in-line filter in my opinion.

TwoTired · « **Reply #16 on:** July 05, 2011, 06:14:09 PM »

If the carbs are at stock settings, and you have stock exhaust, you will need the air box and filter to make it run right. Sorry, no shortcuts.

SurfinBird · « **Reply #17 on:** July 05, 2011, 08:19:24 PM »

You guys were dead on. I pulled the tank, removed the petcock, shoved a screwdriver in there and pulled out the old screens collar. I put the petcock and new screen on, cut some new fuel line (minus the inline filter) and started it up. It idled at 1100, i was able to rev it to about 6000. I took it for a short spin, it ran really well, but it did the same thing. This time I think it may actually ran too low on gas because I don't have much fuel in it. I had to run it on res the whole time. One odd thing is the #2 overflowed, that hasn't happened before, just the #2. Another thing is it seems like the fuel flow was slow coming out of the tank after I put the screen in, i'm not positive since I never really checked the flow before. Is there a spec on how much fuel should be flowing out of the tank? I probably have to pull the carbs and check the lines feeding the carbs for blockage. I may not have fixed it entirely, but i'm chipping away at it.

camelman · « **Reply #18 on:** July 05, 2011, 08:47:09 PM »

Clean the carbs and check your timing/points.

BeSeeingYou · « **Reply #19 on:** July 05, 2011, 09:36:01 PM »

An overflowing carb is usually junk keeping the needle valve from closing or a float hanging up. You may still have some residual particles in the system. Did you give the tank another flush before you installed the new filter and petcock? With the old filter stuck in there you probably never got all the crude out as the old filter would stop it from draining out. Get your tank spotless and keep it that way and you will have far fewer carb problems. Once you get the system purged of particles you should be in much better shape.

The F bikes (at least mine) will go on reserve with at least a gallon + still in the tank so it's no surprise you had to run on reserve.

SurfinBird · « **Reply #20 on:** July 11, 2011, 01:08:09 PM »

I had a thought. Would I get a fuel starvation problem if the gas cap breather vent was plugged up? If I read correctly the breather is on the cap on this model. The tank was pretty rusted when I got it, and I didn't pay a lot of attention to the gas cap when I was de-rusting.

bollingball · « **Reply #21 on:** July 11, 2011, 02:40:55 PM »

As far as the gas cap yes (vent in cap) but keep this in mind. If the tank is full there is very little air at the top so with the vent plugged up the engine will act up a lot faster. With 1 gallon of gas a lot more air in tank it takes a little longer to use up the air and start fuel flow issues if reserve is OK. ++1000 in line filter no need for any thing else.

Once everything is clean (AGAIN) start with your 3000 mile tune up and as TT said "sorry no shortcuts" and do them in order.

Ken

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Author Topic: A little help.... (Read 2450 times)

bollingball