Topic: still backfiring....

[Jersey550F]

Ok,
After my top end rebuild I am still getting backfiring but can't get her to start.

-I've checked the valve clearances

-timing is perfect

-getting spark at TDC at the correct cylinders

-checked to make sure all of my wiring is correct (plugs/solenoid)

-checked the carb bowls getting plenty of fuel

-Compression is low (80's) but that's w/ new rings (cyclinders were de glazed) I should still be able to get her started w/ that shouldn't I ?

My only questionable item is the fact that I cannot get my t-chain tensioner screw loose.  The whole assembly turns (screw and but) and when I use a wrench to hold the nut in place I cannot get enough torque on the screw to break the nut loose. Shouldn't I be able to get the bike started w/o the correct tension ?

This is my last ditch effort before I ship her off to a mechanic so any help will be much appreciated. Thanks...




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[Bob Wessner]

-getting spark at TDC at the correct cylinders

Don't know if it is 100% of your problem, but if you set the timing at true TDC, it is retarded. The idle timing should be set to the "F" mark, not TDC. TDC is for setting the valve clearance.

[Jersey550F]

Sorry, I should have been more specific. My timing is set to the F mark.   What I meant to say was,  I am sure that I am getting spark when the piston is at the top of it's rotation, therefore eliminating the possibility of my cam being off 180. Thanks though, appreciate the response.

[kghost]

Just cus your getting spark with the piston at top doen't mean your cams not 180 out.

Not saying it is, just pointing out that they are not one and the same.

Spark happens when the cam on the crank opens the points. It could care less what the cam position is.

[Badboy]

I will agree with Kghost, the spark is set by the crank and if the cam were off a tooth or two it could cause problems,but if the cam
was off 180 it would not start at all. Maybe that is why you are not getting better compression. It seems to me that you should be getting a lot better compression than that. I am a master machanic on autos[thirty years] and have done a lot of repairs on about anything that runs ,but I would have to see it first hand to realy get a handle on your problem. I have a feeling that your cam is off a couple of teeth ,that would put a crimp on things. I can tell you how to check your cam timming.  Take out your valve caps for #1 and #4. Now turn the engine untill #1 is at tdc. Is the intake and exhaust both closed? [You can feel the play in the rockers]
Now ,rock the engine back and forth a little,do one of  the valves on #4 [depending on which way you turn] start opening right up? Turn both ways if they are equal [turn a little one way then the other way they will both start to open one in one direction and the other  the other way ]? If the cam is timed right both valves will like be on a peak. If you have to turn more in one way to get the valve to open that the other way it is not timed right  I do not know how skilled you are ,but this procedure will check the cam timming. This procedure applys to a twin as well ,in fact any engine sixes v8s the whole shabang. I am trying to think, the sohc 4
has a spark on two cylinders each rev, so therefore I think that you have a cam that in a little off.  [compression reading]?

[Jersey550F]

Thanks for the response. I guess I will tear down the head once again and confirm that I am not off by a couple of teeth on the cam. How can I be sure once I have the head off that I am on the right tooth? I'd like to confirm while I have it apart.

[057 adnoh]

did you open the throttle wide open when you did the compression test? if you did not the psi would be around 80

[TwoTired]

How can I be sure once I have the head off that I am on the right tooth? I'd like to confirm while I have it apart.

Well, you could try following the instructions in the Honda Shop manual, Haynes, or even the clymers.  They even have pictures!

[Jersey550F]

Thank you for the insight Lloyd. Unfortunately I only own a clymer manual and having followed the instructions to a "T", I am still in this mess.  Maybe I should try some different manuals and see the variance.  After all, I have already found two mistakes in my clymer manual.

[TwoTired]

I've found several errors in the clymer.  I hardly ever use it anymore.  The one printed in 75 was much better, IMHO.  Though, the cam install seems clear enough in both.  But, I've done the cam several times, too.  Both the Haynes and the Honda manual have much clearer pics and instructions for the cam install for sure.

You gonna take the head back off to check for bent valves and piston contact?

[DRam]

Check illustration #26 on page 58 of the Clymer manual and surrounding text for a description of how to correctly install your cam.  Mine is the 1978 edition, if yours is different the illustration may be in a different place.

[hymodyne]

the first time I re-assembled my engine, I was 180 degrees off. I had spark, but could only backfire and smoke. I re-checked the notch on the end of the camshaft, making sure that it aligned with the top of the cylinder head body. 

[DRam]

I just found out how to post images.  Let me know if you need the illustrations spoken of earlier and I'll post them for you.  Ain't it amazing what you can do when you read the directions?


DRam

[Bob Wessner]

Ain't it amazing what you can do when you read the directions?

Seems like I mumble that to myself at least once a week. 

[eldar]

I didnt see this asked so I though I would just in case.
 Did you do any work with the carbs? Do you have the spark plug leads on the correct plugs? Sometimes you just never know.
You get in a hurry cause you are so happy to almost be done that you forget something.

[DRam]

Ahhhh.  Good point.  What's that they say?  Always check the simple stuff first?  In fact there's a post about that somewhere.

[Badboy]

I made a misstake on the procedure to check your cam timming[works on any engine]. It would be #1 and #3 ,not #1#4. It would be the one in the middle of the firing order,example: 1432 it would be #3. The same on any engine ,you have to look at the firing order.#4 would be getting ready for the intake stroke when #1 is at TDC. So if you are in a situation where you need to check cam timming you can do this way. Sometimes the ones that design these rigs make a misstake and put a mark of some kind where you can see it without to much trouble ,but that is not always the case.

[bryanj]

Favourite problem was to accidently unplug one of the contact wires (yellw or Blue) down by the rear brake pedal so that its only trying on two cylinders.

[dpen]

Haynes manuals are good, Clymers are good for hanging from a piece of string on the toilet door.