Topic: cb350- issue after rebuld...

[mikedialect]

So, I rebuilt/refreshed a 71 cb350. I got it all back together, did the valves, points, timing, plugs, plug caps. I still haven't got it running. It's backfiring out of the carbs or backfiring out of the pipes if I have it choked.. I've got spark and gas, so I removed the air filters (maybe dirty?). Still only back firing. I'm wondering what the hell it could be. The last one I did- same situation- not the same results.

Any thoughts?

[754]

Can the advance cam go in more than 1 postion??

[mikedialect]

Can the advance cam go in more than 1 postion??

Maybe? I'll have to give that a look tomorrow. I guess- since I wasn't thinking about that.... maybe the wires are wired wrong IN the point assembly.

hmmmmmm

[cben750f0]

excuse my ignorance, but i know that you can wire the coils on the 750 wrong, and that has the same effect, so are the coils wired the right way round?

peace

[mikedialect]

Can the advance cam go in more than 1 postion??

It can't actually. Tried swapping a few things around and I'm still getting nothing.

[mkramer1121]

Is the needle clip position set correctly on the carbs?

[mikedialect]

Is the needle clip position set correctly on the carbs?

Should be. I took them apart and cleaned them. Pretty sure I got them back in right.

[heffay]

flip flop the coil wiring... that seems to be the usual cause when things like this happen.

it happened to me the last time as a matter of fact 

edit: if its trying to fire that means you did something right 

[mikedialect]

flip flop the coil wiring... that seems to be the usual cause when things like this happen.

it happened to me the last time as a matter of fact 

edit: if its trying to fire that means you did something right 

I will give that a go.... I've been feeling defeated all night. I have to get this rolling!

[cben750f0]

same as me, just had the coil wireing mixed up..

peace

[crazypj]

Can the advance cam go in more than 1 postion??

It can't actually. Tried swapping a few things around and I'm still getting nothing.

 I think you'll find it can be fitted 180 degrees off.
There is a mark on the top edge of cam that looks like someone hit it with a chisel and theres either a hole or semi circular cut away on the advancer body. They should line up. you can twist the cam and lift a the same time to remove it from the bobweights. This information is NOT in any service manual, I worked it out from working on Honda's in the late 60's

[754]

I remember getting paid by a journeyman auto mechanic to discover this when he changed to points in  his Harley...LMAO.. I never took any automotive or engine courses ever..

[mikedialect]

Can the advance cam go in more than 1 postion??

It can't actually. Tried swapping a few things around and I'm still getting nothing.

 I think you'll find it can be fitted 180 degrees off.
There is a mark on the top edge of cam that looks like someone hit it with a chisel and theres either a hole or semi circular cut away on the advancer body. They should line up. you can twist the cam and lift a the same time to remove it from the bobweights. This information is NOT in any service manual, I worked it out from working on Honda's in the late 60's

Interesting. I'm not sure if that mark will still be present- as I have cleaned and refurbed the advacner, but I will definitely give a look-see

[CBGBs]

Mike,

   I had my 350 worked on at a "reputable" shop and I had to return it because it seemed the cam was 180 degrees off. I havent' quite gotten my head around the physics of it but the thing would barely run. It just wanted to backfire if it would even ignite. The left piston should be up on compression stroke and the dot on the end of the cam is top and the horizontal line on the cam sprocket is parallel to the head surface and mars is in its waxing phase.

[crazypj]

I remember getting paid by a journeyman auto mechanic to discover this when he changed to points in  his Harley...LMAO.. I never took any automotive or engine courses ever..

me neither, had to figure it all out the hard way. (now I teach it to others though)

[mikedialect]

i cant seem to see a mark.... I see that slash, but it does not line up towards the 'cut out'

[mikedialect]

also, I removed the tank so I could swap the plugs to the other sides. Still didn't pop over.

[Raul CB750K1]

Let me share my experience with CB350 with you guys.

Before I rebuilt the engine I got all the possible info I could, Honda and Haynes manuals, and also several articles from Classic & Motorcycle Mechanics (Glenn have now them all if you are interested). Well, in one of the articles of CMM, they said that the official shop manual was wrong with regard to the camshaft bolts, they should be installed the other way round.

Camshaft bolts, not only are high tensile, but also are different. One is threaded all the way, the other has a "pan", a part of the bolt not threaded from the head. Since I read that I wrote down a mental note to myself: "never forget this when the time comes".

Several months later came the time, and I didn't forget about it, and even when I tried to install the bolts opposite to what the Honda manual said, there was no way. If one went in, the other was out of alignment. I was positive I should be doing something wrong, because if the skilled people at CMM found the mistake and published it, there should be a mistake. But the fact is that it was impossible to install the bolts that way. BUT, if I turned the camshaft sprocket 180º, they would go just fine. The way to know which bolt goes where was that the bolt with the "pan" had to go on the sprocket hole that was not threaded, and vice versa. Seems that the bolts are not 180º apart but a different angle -say 177º-, so if you put them wrong they will never align. That is, Honda designed them in such a way that you can not install them wrong even if you want, that whay the "TOP" mark on the sprocket will set the lobes in the right position.


I don't think there is a position for the advance mechanism. Pistons are 180º apart and so should the lobes on the advance mechanism, so it shouldn't really matter which way it goes in. If memory serves me, there is a slot in the camshaft for the mechanism to go in so there shouldn't be more than one way to install it, but it has been a few months since I did it. I put my mouth -not my money- for crossed coil wires, but considering the experience you have with CB350's, I don't think it is such an obvious mistake.

[mikedialect]

and I did double check the coil wiring as well. She's not even backfiring anymore.

[754]

Is there a chance that if you used 2 regular bolts without the shoulder/pan (and managed to get them in), that it could have got assembled 180 deg out??

[mikedialect]

Is there a chance that if you used 2 regular bolts without the shoulder/pan (and managed to get them in), that it could have got assembled 180 deg out??

I don't follow- what is a shoulder/pan?

[754]

Bolt that is unthreaded below the head.. if it is threaded all the way it is a looser fit.

[mikedialect]

Bolt that is unthreaded below the head.. if it is threaded all the way it is a looser fit.

on the points plate?

[Raul CB750K1]

I believe he is talking about the camshaft sprocket. With the original bolts there is no way to install the sprocket in the wrong position. He says that if you replaced the bolts with regular bolts threaded all the lenght there are chances that you managed to install the sprocket reversed -not side to side but with the holes facing the wrong camshaft mounting hole-

I must add that these bolts need to be high tensile bolts, so it's either original ones or nothing. I don't think you can use pan bolts on the points plate. The plate is so thin that the bolt wouldn't thread all the way in.


You didn't need to remove the gas tank to reverse the wires; it was enough to swap them at the points plate.

[mikedialect]

I believe he is talking about the camshaft sprocket. With the original bolts there is no way to install the sprocket in the wrong position. He says that if you replaced the bolts with regular bolts threaded all the lenght there are chances that you managed to install the sprocket reversed -not side to side but with the holes facing the wrong camshaft mounting hole-

I must add that these bolts need to be high tensile bolts, so it's either original ones or nothing. I don't think you can use pan bolts on the points plate. The plate is so thin that the bolt wouldn't thread all the way in.


You didn't need to remove the gas tank to reverse the wires; it was enough to swap them at the points plate.

I did because they aren't very pliable. Either way- I drained the battery, so I'm waiting for it to charge before I go at it again.

[mikedialect]

well, as far as I can tell- and per sprint66/steve's advice- it has to be the valve not closing. So, it looks like I will be taking it out again and giving the head a look. She was leaking pretty badly at the cylinder to lower and rocker to cylinder- so I'm not sure what I'm going to do. I have a spare runner but I really wanted to keep the engine numbers correct on this as I wanted to get it running and do a full repaint/polish.

[DarkRider]

You might be best off to throw the runner into the bike for now and perhaps build a bench testing set up to try to get the original engine running again.

[mikedialect]

You might be best off to throw the runner into the bike for now and perhaps build a bench testing set up to try to get the original engine running again.

I'm in no real hurry to get it riding. I'm really most interested in figuring out what the problem I also just got a roller that I can throw my spare in... so, I'm just going to drop this out tomorrow and see if I can swap out the head and see if that helps.