Honda "Express"ing difficulty...

James Foster /

Sorry for my lame pun on the subject, I just had to do it. Anyways, I just got my Honda express engine bored out .40 over stock, and just finished installing it today. Well, it runs, but it has a few issues. It idles, but only because I put the idle up higher than it's supposed to be to keep it running. The idle mixture screw is almost all the way screwed in, otherwise the engine dies. It doesn't have as much "get up and go" as it used to, and when I do get up to a good cruising speed and let off the gas, it keeps going. I checked the throttle cable and linkage, but all is moving well there. And it gets hotter that usual as well. Also, while I was in the process of keeping it running, it started dying, then when it stopped, it made a small, low-tone ding type of sound. I mean, I know I'm just breaking it in, but something just ain't right here. I'm trying to be careful and break it in properly, but it's hard when it isn't running right. Can anyone help with this matter? Please answer ASAP, I am in a sort of "rush" to get it to a normal, average running condition.

Thank you,

JF

Re: Honda "Express"ing difficulty...

Lame puns are great. Why you would want to bore out an express is another question, but I will roll with it. I think we need to know more.

-Did you make any other changes, intake, carb, exhaust.

If you are using the same carb it makes sense that you would have to screw in the idle further than usual more cylinder = more air needed

Re: Honda "Express"ing difficulty...

James Foster /
jf OP

Well, there was significant scoring on the cylinder walls, and on the piston, so I decided to bore it .40 over(a very small amount). Nothing else was changed, but I see you're point about the carb. Unfortunately, my carb doesn't have a replaceable jet, so that's out of the question. Although I could enlarge the jet that's in there SLIGHTLY, but I'd be afraid that I would screw it up or something. Oh why do these Honda's have to be such a pain, always have some little issue or another...

Or is it just me? :/

That would be scary, but theoretically possible nonetheless...

Any more suggestions?

JF

Re: Honda "Express"ing difficulty...

_And it gets hotter that usual as well. Also, while I was in the process of keeping it running, it started dying, then when it stopped, it made a small, low-tone ding type of sound_

That would really worry me... nevermind about a crappy idle. I would have already pulled it apart and examine it carefully, paying particular attention to the bore and piston condition.

Re: Honda "Express"ing difficulty...

James Foster /
jf OP

That's what I was thinking too. :/ I'll look at it tomorrow as soon as I get the chance to get a good look at it.

JF

Re: Honda "Express"ing difficulty...

Jonas Quimby /

Some of the Expresses had a removable jet in the carb. I believe it was 1979 or some such year that had them. That might help your problems.

Also, it would be a good idea to pour a dabble of oil into your gas tank. The oil injector is only injecting enough for normal running, not an un broken in overbore. Not enough oil means running hot, and that's not good.

I'd also take a peak at your ignition timing just to make sure it's right.

Re: Honda "Express"ing difficulty...

James Foster /
jf OP

Well, what I did was I by-passed the injector for now and put a pre-mix in there, just to be on the safe side. But I thought that you couldn't change ignition timing on Honda expresses? Oh and my model is a 80' NC-50, if that helps any.

JF

Re: Honda "Express"ing difficulty...

Jason Luther /

you said you overbored the cylinder and everything else was the same, did you get an oversized piston? or are you using the same piston?-jason

Re: Honda "Express"ing difficulty...

James Foster /
jf OP

Oh yea, I got a new Weisco piston to fit the bore and rings for it as well. The other reason I decided to go ahead and bore it out a little was because my original piston's skirt broke...:/

Ah and a update on the express; Well, thankfully it didn't seize up when it made that "sound" earlier. I think it just overheated a bit, which BTW is still a slight problem. Overall performance isn't really something to smile about right now, but it does run. And it still acts like the throttle is getting stuck(even though the throttle cable and slide move quite freely), but only while it is in motion. The idle is fairly smooth, but is still set a bit high since otherwise it'll die. And while it's on the stand, it'll rev itself up a bit high all by itself, unless I have the brake on. I know that I should lower the idle until the rear wheel stops moving, but right when I lower it to that point, it gradually dies. So there are still issues, the worst one being that it keeps going when I let off the throttle. But at least it does run, for now. Any more suggestions? Thanks guys for you're help so far, I really appreciate it.

JF

Re: Honda "Express"ing difficulty...

carb troubles.. adjust the float and cables and examine all the mechanical internals for smooth operation .. Until the carb is in perfect working order, diagnosing any other apparent problems is difficult or impossible to do with confidence.

Re: Honda "Express"ing difficulty...

James Foster /
jf OP

True that Joe, I'll check that tomorrow, since it's raining outside. :( It just seems like I've cleaned that carb half a dozen times already...

But, you never know...

JF

Re: Honda "Express"ing difficulty...

Jonas Quimby /

Your carburator is out of adjustment. You need to follow the adjustments in the manual pretty closely, even when they seem to go against what you think will help. If the carb's not right it will bog down, accelerate like mad at an idle and then die, etc.

Re: Honda "Express"ing difficulty...

_it’ll rev itself up a bit high all by itself_

_it keeps going when I let off the throttle_

not a lot to say about it .. something or other about the carb seems to need attention.. idle air flow or choke or float level or something aint right.

Did you measure the new piston and the bore? Normally, the bore should be about 0.002 larger in diameter than the widest part of the piston skirt.. near the very bottom of the skirt, crosswise from the trunnion pin.

Good to hear there's no evidence of seizure. Gap the rings to be sure they are not binding when the engine gets hot.. A ring's end gap when it's slipped into the top of the bore should be near 0.008 inch, at least. Too little gap can make them bind and cause lots of friction (or worse).

And since that's a brand new setup with the new rings, and piston and bore, the heat build up might be explained with normal heavy wear while the parts break-in.. Extra friction could also explain the high idle speed needed to keep it running, although it seems like there is way too much friction somewhere.

Re: Honda "Express"ing difficulty...

James Foster /
jf OP

Hmm, good point, I'll check the carb first, see if that helps. If not, I'll pull off the bore and check the gaps again, just to make sure. Thanks for the advice Joe, I just hope I haven't screwed something up already...

Jf

Re: Honda "Express"ing difficulty...

one other thing.. A bore is supposed to be perfectly straight and round. We are talkin' thousandths of an inch.

It's not easy to overbore cylinders by tiny amounts so sometimes they hone it instead. A hone can take off a lot of meat in a hurry. Unfortunately, honing is far less accurate than is using a boring bar. It's easy to put a taper in a bore with a hone..

Careful examination and measurements will tell the story ..

Re: Honda "Express"ing difficulty...

James Foster /
jf OP

Hmm, interesting point...

I shall investigate and measure the bore, just to make sure the people that I had to do the job did it right.

JF

Re: Honda "Express"ing difficulty...

James Foster /
jf OP

Well, just got back from measuring everything, all checks out. Carb checked in multiple areas, no problems. Electrical is working good, and compression is good. Still though, the idle, and the mixture screw are screwed in almost all the way in to keep it running. And, after running it for over half an hour(series of idle-medium RPM's), it for not apparent reason just starts to die, making yet again strange low-tone pinging noises while dying(like someone very lightly taping on the cylinder head with a small screwdriver). I believe it is overheating, but I don't think it should be. Can someone tell me how to break-in this engine properly, before I screw something up on it?

Thanks,

JF

Re: Honda "Express"ing difficulty...

That pinging is a mystery.. and finding it's source seems far more important than tracking down the reason for the bad idle.

If there was no head-work compression ratio should be nearly the same... the head is not packed with carbon .. The new piston could be making contact with the head?

Rod bearing condition is unknown (to me) but if they're bad enough, who knows.. the noise would resemble a pinging or knocking.

But this noise happens only after it's warmed up and the result is the engine dies. I'd say its all related. Something is changing in the hot engine. Friction rises, a knocking noise develops, idle slows and the engine finally dies.

Something mechanical ain't right. I would not give up searching for it's source and continue the break-in as if everything were ok just yet.

Try one little test.

Remove the head, fasten the cylinder back down with a couple head bolts (use a stack of washers or tubing to "shorten" the head bolts).

Turn the flywheel so the piston rises and slightly passes over TDC. Then hit the piston crown with the heel of your hand. If you hear a distinctive "click" the rod bearings are probably gone. That could be the source of the pinging noise.

Re: Honda "Express"ing difficulty...

James Foster /
jf OP

I see where you're going, but it only pings when it's been run for over 30 minutes. Something to do with it getting really hot makes it do that, and only then. I did replace the upper connecting rod bearing when I replaced the piston, so the upper one shouldn't be the problem. I might end up trying out that test anyway though...

Oh, and here's something I forgot to mention earlier; I by-passed the oil pump and went with pre-mix because of the new 41mm size engine, and I took out the oil pump drive shaft so that the pump wouldn't sit there turning without lubrication. But, I noticed that while it was running, the oil pump was acting and sounding like a fish pump. So I connected the oil lines back to where they were, hoping to stop the problem. But it still does it to an extent through the oil tank. So my question is, should I reconnect the oil pump, or should I find a plug of some kind to fit in the oil injector hole?

JF

Re: Honda "Express"ing difficulty...

Jonas Quimby /

Did you get around to checking your timing?

The timing on the Express IS adjustable to a degree. But if it's too far off you need to replace your points.

Having your timing off can definatly cause simalier problems to what you're seeing.

As for the oil injector, what most people do is they leave the oil pump in place, and then connect a loop of oil filled tubing from the output to the intake. Gives the injector something to circulate. Then they just cap off the oil line nipple on the engine.

Also, what ratio are you running on right now?

And finally, pinging is usually a sign of pre-ignition.

I'm not surprised that ti only happens when the engine is hot.

Re: Honda "Express"ing difficulty...

James Foster /
jf OP

The question is, HOW do you adjust the timing? I know you can make the point gap bigger or smaller and that will change it a little, but is there another way to do it? Good idea for the oil injector, I might try that. I believe I'm running a 32:1 ratio right now for the fuel/oil mix. Oh and would timing affect the idle because it only idles for a little over half a minute. Could that be the cause? Oh and I went ahead and put the shaft back in the oil pump, and it runs a LITTLE better, but still having idling and acceleration problems. Oh and thanks for the input, I appreciate it.

JF

Re: Honda "Express"ing difficulty...

Timing adjustment is limited to setting point gap on these engines if the stator plate (the thing the points are mounted on) cannot be moved and the 'cam' on the cranksaft that the point's lever/pad rides on is in a fixed position.

I don't see how boring the cylinder and a piston change would change timing.. but who knows.. maybe something got tweaked during the process.

Another possibility that could explain symptoms of a pre-ignition type "ping" is a high compression ratio. This could be the result of a piston change if the new piston crown protrudes further into the combustion chamber than the old piston did.

Another possibility is compression ratio was raised by whoever did the cylinder work.. perhaps they cut something off the top of the cylinder, shortening it. Another possibility is the cylinder base gasket is missing (?) or needs to be thicker.

To test the possibility that compression ratio is too high, use a very thick head gasket or more than one head gasket. Use something near a total thickness of about one millimeter more than what is now there. This will lower compression ratio by a bunch, adding about 1.2ccs to the volume of the combustion chamber. If the pinging stops, you're on the right track..

This lower compression ratio might stop the ping.. however it could do this by just hiding and masking the source of the problem.. a misadjusted, very advanced ignition timing. In other words, it might not ping anymore but compression ratio was not the source of the ping.. excessive heat due to advanced ignition timing was.

So, in any case, check timing with a timing light or with the depth gauge method through the plug hole, or however the owner's manual instructs.

Re: Honda "Express"ing difficulty...

James Foster /
jf OP

Good idea, will look at timing tomorrow. Oh and I put Permatex 2 gasket maker in place of the old base gasket. Could that have something to do with the problems I'm facing?

JF

Re: Honda "Express"ing difficulty...

depends..

Permatex 2 doesn't harden so maybe it blew out under pressure.. and maybe you now have serious leaks down there. Anyway, it's not meant to replace a cylinder base gasket..

The absence of a base gasket will raise compression ratio.. knowing to what degree it was raised requires that you do the math.

And no gasket maker will provide a particular, correct base gasket thickness except by accident.

Re: Honda "Express"ing difficulty...

James Foster /
jf OP

So with a higher compression ratio it won't run as well? Could the lack of a real gasket be my problem because it isn't as thick? If so, I'm gonna need a new gasket...

JF

Re: Honda "Express"ing difficulty...

High compression ratio heats the mix and encourages a fast air:fuel mixture burn.

If the burn is too fast, peak cylinder pressure occurs too early and heat builds up further, encouraging an even faster burn .. the end result is detonation .. a severe strain on the engine accompanied by knocking. (This is how heat puts strict limits these air-cooled engines' power outputs)

A base gasket physically raises the cylinder up. The piston can't compress the mixture as much as it would without the base gasket. So a base gasket is one of the things that determines compression ratio.

The change from a stock 40mm cylinder to 40.4 mm bore raised the compression ratio a bit.

If your combustion chamber volume is 8ccs, the rise in CR (compression ratio) went from 7.28:1 to 7:40 to 1 . This is a minor increase in CR and can be disregarded, imo..

But add no cylinder base gasket to the equation and who knows.. you might have raised CR by enough to enter the heat problem zone...

Re: Honda "Express"ing difficulty...

James Foster /
jf OP

Interesting point. It could account for it having to have a high idle, and not being able to run it for over half an hour. It's also difficult to start though, and still has that "like throttle is sticking" issue while in motion. Not sure if a lack of a base gasket is the cause for all of these symptoms, but it might help to put a real one on anyway.

Thanks for the info,

JF

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