Topic: 78 cb750 F2- some issues- where to go from here...

[mikedialect]

Well, I've been having the wrong side of luck this summer. Noob should have bought a new bike instead of these fellas. Some of you might have seen my post in the other bikes category about my 350. Well, since that bike stopped running I thought I would finally try and tackle my 750 and get that running strong. Now, I'm at a loss, yet again.


So, my 78 750 F2 is a bear. It chugs and stutters in all gears and it simply will not go over 50 miles an hour. I brought the bike over to my uncles house a few weeks ago to see if he had any advice. He basically- non conclusively as well- determined that it felt like the bike was being starved of gas and then recovering over and over. We thought for certain that a carb clean would do the trick. I thought that some rust might have accumulated in the tank and was making it's way into the carbs blocking the jets. Today I took the tank off, drained the tank and there were a few floaters in there, but they were microscopic at best. Then I went and took the carbs off to see just how bad they were. They were absolutely spotless. The PO that I picked it up from this winter said he had done a clean on them, but I was starting to doubt his tale. I confirmed that he did in fact clean them.

Here's a better description of what is going on. I rode the bike on and off at least once a week since march- it was f&*king cold, but I rode it and ran a few cans of sea foam through it. The chugging problem is an all speeds issue with the worst chugging happening at the beginning of acceleration. Like I said before, the bike simply will not go over 50-55. Here is the thing- the chugging problem has gotten worse since this march. So, I decided that it's simply not ridable the way it was working and I started to tear things down. The two things I thought it could be were ruled out. The only thing that was suspect was that on carb #2 the accellerator diaphram was looking a bit spotty. It wasn't completely torn up, but on it's way. I talked to a few folks about rebuild kits on the 78 and they simply don't make them, so I don't really know where to turn for a replacement diaphragm. As of now- I don't know where to go from here. I was hoping to get this bike rolling so I could get the engine out of that other bike to see what went wrong. Now I'm grounded two fold wondering what to do.

Any ideas would be appreciated! Thanks in advance.

[750goes]

Ok,

pull all your plugs and gap them - then let us know the colours of each plug
check all your plug caps to make sure they are nice and tight, and getting/making good spark on your plugs
take off the points plate and lubricate the advancer unit and check if it is working..
check and readjust the points gap on both sets
do a static timing
check your points wires coming from the points to the coils for any bare wiring

have you done a valve/tappet adjustment, camchain adjustment also ??

keep going it will work soon..

[mick750F]

   Can you contact the PO and ask them if they removed and cleaned the slow jets and made sure that all carb passages were clear? Did they set the air screws and sync the carbs after cleaning? If you can't verify this from the PO then you should check them yourself...maybe check them anyway...as well as doing a complete tune-up just so that you know where you stand.

   Carb kits are available from Honda AFAIK as well as the pump diaphragm/rod.

Mike

[mikedialect]

Ok,

pull all your plugs and gap them - then let us know the colours of each plug
check all your plug caps to make sure they are nice and tight, and getting/making good spark on your plugs
take off the points plate and lubricate the advancer unit and check if it is working..
check and readjust the points gap on both sets
do a static timing
check your points wires coming from the points to the coils for any bare wiring

have you done a valve/tappet adjustment, camchain adjustment also ??

keep going it will work soon..

I put in a new set of plugs and gapped accordingly. I wasn't fouling on any of the cylinders. Plugs looked normal use.

I went through the caps a while back, but I will do so again just to double check.

Tomorrow I am going to get timing, points adjusting done and check those other points related issues looked into.

I haven't done a valve adjustment or cam chain yet. Tomorrow as well.

I will definitely give these extra little things a go tomorrow and report back.

[mrbreeze]

Most of the tune-up items mentioned here should be done before the carbs.If everything is up to snuff and you do the valve,cam chain,ignition adjustments....thats when you go to the carbs.If you are sure they are clean and adjusted properly,your last step is carb synch. It takes a bit of time,work,$ but if you like these bikes,it will be rewarding in the end. Good luck and post back when you have satisfaction!

[johnny-from-bel]

While you are at it, check the ignition advance weight. See it they can move freely.

[mikedialect]

most definitely a points issue. PDPimp came over today and he helped sort through some of the points problem. It needs a touch of fine tuning still (probably new points or a dyna!), but it's running better than ever.

Now I just have to tackle the NEW issue that rose today. I'm now leaking gas like crazy out of carb #3.

[johnny-from-bel]

I'm now leaking gas like crazy out of carb #3.

That is probably a stuck floater. Tap it with a screwdraver and see if it comes lose

[mikedialect]

I'm now leaking gas like crazy out of carb #3.

That is probably a stuck floater. Tap it with a screwdraver and see if it comes lose

I was reading through earlier and the same was suggested and I did so. Took care of it so far.

Now, I think I'm going to have to get down on those air screws and play around. My idle sits AWESOME when it does actually get down to 1100-1200, but it doesn't want to drop after going up a few gears and coming to a stop light. The idle just sits up around 2K+. Not sure what the cause of that is... BUT I'm ordering up a dyna ignition so i don't have to fiddle with those points again.

[750goes]

mikedialect,

your problem is more than likely sticky slides, sticky cables, or an air leak around the carb manifolds - try and sort those out will help..

not bagging the electric ignitions - but well adjusted points have been around for a long while - and are easy to maintain - and become seconnd nature - your electronic dyna dies - and you start pushing....

[cben750f0]

i agree with 750goes, but i have a dyna, and a full points plate under the seat!!!, marked with the points cam, so it dops straight on, and away we go.... theF's have a nice under seat tool box..

peace

[mikedialect]

mikedialect,

your problem is more than likely sticky slides, sticky cables, or an air leak around the carb manifolds - try and sort those out will help..

not bagging the electric ignitions - but well adjusted points have been around for a long while - and are easy to maintain - and become seconnd nature - your electronic dyna dies - and you start pushing....

I'm going to give the carb boots some attention today and see if it is a leak.

How often would you say that those dyna's bite the dust? Is it a pretty common deal or are we just talking about the nature of electronics?

[750goes]

from all reports and mentions they get -they must be reliable or they would not sell...

[cben750f0]

i have done over 30000km  with mine, and have never had a problem.... the only thing you have to be careull of is when fitting them you dont wire them up wrong... other than that they are pretty bullet proof.... there isnt and moving parts other than the advance mech.

i think they give a better spark also... my bike seemed to run a bit cleaner with the dyna, than with the points....

hope this helps

peace