Topic: 1976 CB750A Project Bike (was New Guy with New Project)

[Old75_ratafe]

Nice looking bike and great cleanup on the motor! don't have any suggestions about the bogging issue, but I'll be watching as I'm sort of in the middle of getting my '77 A back together as well. I'm afraid mine needs new clutches tho...pulled the pan as part of trying to figure out why it won't go into high gear, and found little chunks of non-metallic stuff. Great to see another Hondamatic owner here...the Hondamatic.com forum died not long ago..

I thought the honda matics had a torque converter?

[mrbreeze]

I'm betting that all you need is a carb sync if everything else is in order. The carbs must be in sync or else the cyliders are fighting each other. If you plan to keep this bike or get other multi carbed bikes....do yourself a favor and spend the $$$ for a manometer. I've had gauges and I've heard horror stories about mercury columns but The $100 I spent on the Morgan Carbtune was well spent and I'll bet you won't regret doing the same. Good luck with your automatic and I must say it looks good after the engine R&R.

[Grnrngr]

Nice looking bike and great cleanup on the motor! don't have any suggestions about the bogging issue, but I'll be watching as I'm sort of in the middle of getting my '77 A back together as well. I'm afraid mine needs new clutches tho...pulled the pan as part of trying to figure out why it won't go into high gear, and found little chunks of non-metallic stuff. Great to see another Hondamatic owner here...the Hondamatic.com forum died not long ago..

I thought the honda matics had a torque converter?

It does.. but there are also friction plates in the trans..

[Rdlbs]

I'm betting that all you need is a carb sync if everything else is in order. The carbs must be in sync or else the cyliders are fighting each other. If you plan to keep this bike or get other multi carbed bikes....do yourself a favor and spend the $$$ for a manometer. I've had gauges and I've heard horror stories about mercury columns but The $100 I spent on the Morgan Carbtune was well spent and I'll bet you won't regret doing the same. Good luck with your automatic and I must say it looks good after the engine R&R.

I agree that it will need a sync.  I'm not sure that's the weakness right now though.  It runs so very well when I am running it by filling a funnel and hose with gasoline and so eratically on the tank.  Watching it yesterday, I would notice the clear fuel filter filling up and then draining and then filling up again.  This fits the profile of the engine running well off and on while running on the tank.  I'm beginning to think that the gas tank is not vented properly and so it develops a vacuum inside that tank which will not allow the fuel to flow evenly. Does that make sense?  The tank must be vented someplace, especially since these bikes are gravity fed rather than fed by a fuel pump. If so, where is the vent?  I'm going to run it this afternoon without the gas cap on to see if that makes a difference.  Thoughts?

I have a friend at work who builds race bikes.  He will sync the carbs for me when I get ready.  Otherwise, I would indeed purchase a good gauge.

[Old75_ratafe]

I thought the honda matics had a torque converter?

It does.. but there are also friction plates in the trans..
[/quote]

Ah gotcha frictions just like a normal automatic.

I agree that it will need a sync.  I'm not sure that's the weakness right now though.  It runs so very well when I am running it by filling a funnel and hose with gasoline and so eratically on the tank.  Watching it yesterday, I would notice the clear fuel filter filling up and then draining and then filling up again.  This fits the profile of the engine running well off and on while running on the tank.  I'm beginning to think that the gas tank is not vented properly and so it develops a vacuum inside that tank which will not allow the fuel to flow evenly. Does that make sense?  The tank must be vented someplace, especially since these bikes are gravity fed rather than fed by a fuel pump. If so, where is the vent?  I'm going to run it this afternoon without the gas cap on to see if that makes a difference.  Thoughts?

I have a friend at work who builds race bikes.  He will sync the carbs for me when I get ready.  Otherwise, I would indeed purchase a good gauge.

The vent is in the cap if you look under it there is a seal.

[Rdlbs]

The vent is in the cap if you look under it there is a seal.

Thank you.  I'll look at it when I get home this evening.  I went to a lot of trouble to clean the inside of the tank, but didn't even think to really examine the cap.  My bad!  I did ride it a little yesterday with the cap loose.  I think I may have hit on the major issue.  However, it is also painfully evident that I need to sync the carbs.  I was wanting to put that off for a while, but now's the time I believe.

I must say that the sensation of riding an automatic is pretty strange.  Since it only has two gears, first is geared pretty high.  And of course, these engines don't make a lot of power in the lower RPM range.  This is going to take some getting used to, but overall I was very impressed with the smoothness of the bike.

[Old75_ratafe]

Yea I can imagine especially on take offs the clutch has a big advantage I would think

[Grnrngr]

heh...yeah, definitely not quick off the line in stock configuration..and taking corners without shifting takes a little getting used to. It is smooth tho..and it has a parking brake so it doesn't creep while you sit at a light.

[Rdlbs]

The real mystery is that I can't figure out why it is now running so well.  I was having trouble with an erratic idle.  I'm still having some issue with the idle, but now it seems to be acting more consistent with a sync issue, which I can deal with.  But the bogging, acting like it is running out of fuel is gone.  The thing is, I didn't really do anything to it.  I rode it a bit with the fuel cap off and that seemed to help.  But then I put the cap back on and left it on.  One thing I did do was to change the routing of the fuel hose coming out of the petcock and down to the carbs.  Maybe that was the issue?  It doesn't make a lot of sense, but that had to be it.

[mrbreeze]

Another thing you may want to do is ditch the inline filter.It should have a strainer on the petcock inside of the tank. I've heard of problems with starvation and the filter was the culprit. Also....you mentioned fuel line routing. That could also cause problems with fuel delivery. It seems you are trying different things to fix the little gremlins that we all have to deal with. This is a good thing. Not only are you learning more & more about your bike but you will also get great satisfaction knowing your bike is running great and you made it happen.I think it is way better than throwing in the towel and putting it in a shop that really isn't familiar with older bikes or even worse...selling it.

[Rdlbs]

I'm betting that all you need is a carb sync if everything else is in order. The carbs must be in sync or else the cyliders are fighting each other. If you plan to keep this bike or get other multi carbed bikes....do yourself a favor and spend the $$$ for a manometer. I've had gauges and I've heard horror stories about mercury columns but The $100 I spent on the Morgan Carbtune was well spent and I'll bet you won't regret doing the same. Good luck with your automatic and I must say it looks good after the engine R&R.

I went ahead and sprung for gauges today.  You're right, I don't think I will regret that.  When I am finished, I'm going to start looking for another project bike, so the gauges will come in handy on future projects also.

[Rdlbs]

Another thing you may want to do is ditch the inline filter.It should have a strainer on the petcock inside of the tank. I've heard of problems with starvation and the filter was the culprit. Also....you mentioned fuel line routing. That could also cause problems with fuel delivery. It seems you are trying different things to fix the little gremlins that we all have to deal with. This is a good thing. Not only are you learning more & more about your bike but you will also get great satisfaction knowing your bike is running great and you made it happen.I think it is way better than throwing in the towel and putting it in a shop that really isn't familiar with older bikes or even worse...selling it.

You know, I was thinking the same thing.  I purchased two different filters.  One is for small engines (and seems to be working well) and the other is actually an automotive type filter.  The automotive type will not allow fuel to gravity flow through it.  Since cars have fuel pumps, most of which are in the gas tank these days, I guess they don't have to be free flowing.  As a matter of fact, I'll bet they are also a check valve, which would introduce some restriction.  Regardless, the automotive type will definitely not work.  Oh and by the way, I did replace the filter screen inside the tank, but I felt that the mesh size was too large to actually protect the carburetors.  I wonder though if this is the concensus of others here on the forum?  Is the secondary filter that I installed superfluous?

[Rdlbs]

Hi guys.  I've been on vacation for a few days, so I haven't had time to update here.  Sometimes, I can have tunnel vision and some of the problems that I have had are most certainly due to my not paying enough attention to detail.  I outlined some of the problems that I was having above.  Part of the problems were due to my needing to synchronize the carbs.  Instead of having my buddy do it, I broke down and bought a set of gauges.  The process was pretty straight forward, but I was still having some intermittent trouble.  It turned out that part of the time, #3 or #4 cylinder was not firing as effectively as it should have been.  By that I mean that they were firing, but not to full affect.  The exhaust pipes from #1 & 2 would be hot, the way they should be, but sometimes #3 would be only warm.  At other times #4 would be only warm.  The idle would be erratic, sometimes going to 1500 RPM or so and other times dropping down so low that the engine would die.

I finally decided that I was going to have to tear some things apart.  I took the bowls off of #3 & 4 carbs and unscrewed the jets and holders (not sure of the right terminology).  Both of these 'posts' with the little holes in them were partially plugged with some sort of debris.  I found this odd, because I just did a complete tear down and rebuild of the carbs.  It finally dawned on me that, although I throroughly cleaned the carbs, I did not tank the aluminum fuel tubes that go between the carbs.  Since the fuel flows from #1 carb through each in succession ending with #4, whatever residue that was left in the tubes was pushed over into the last two carbs which caused them to get partially plugged up.  After cleaning this out, the engine idles smoothly now.  Funny how the littlest things can screw things up.

It's raining here, so I have not had the chance to take a ride, but I'll hopefully get that done in the next couple of days.  I'll report back as to how that goes.