Valve Clatter?????

[Atlas]

This one so far has me stumped, it sounds like one of possibly two things, Here's a bit of info first , I just got her up and running down the road a few days ago , it doesn't run too bad, but I still find it a slight bit boggy under a load especially in high gear going up an incline if I pin it it is a little sluggish, it doesn't spit and sputter or buck, just sluggish.As I'm going through the gears and accelerating I can get the rpm's up to about 7000 and then it sort of goes flat. Also when I accelerate there is a distinct clatter but once the revs are up the noise goes away,but if I crack the throttle I hear it , also if I'm cruising down the road and on level at any rpm it sounds great no weird noises but if it has to work a bit or if I throttle it I hear the clatter.
The intake all seems to be tight, but maybe the filter gasket could be a little better, but there is a gasket there, I know that's not causing the noise , but I thought maybe that was why it was sluggish.
I did adjust the valves , and it could be off a bit but I've checked the clearance and it's pretty close.
I also put a used but good stock exhaust back on it, but everything seems tight .
The cam chain also appears to be good , with no slack.
Could a little leak at the exhaust header be the culprit for the noise? Or is it more than likely the valves being out a bit ?And that's why it's a little sluggish too.
I did a compression test and that seems real good ; #1-180 , #2-180 , #3-175 and #4-185 .
Sorry for the novel , but I'm stumped , any thoughts from the experts?

 

[Nessism]

My guess is detonation noise, not valve clatter. Is the stock airbox installed and what number jets are installed?

 

[Atlas]

Ed , it has the stock airbox and stock jets , I did do a carb rebuild . It seems to idle okay at around 1000 rpm when it's hot and not stall. So you think maybe it's sort of like the same pinging in a car if the timing is off or on low octane gas? I do run High test in it . The sound seems to be coming from the #4 side of the head, it's not a low end engine noise , but almost like a leaking exhaust sound. That's why I thought it was that and not valve noise. The pipes aren't turning colour like it's running hot or lean . Do you think it would be worth trying some high temp sealer?

 

[FLHGSRay]

I agree with Nessism, sounds like predetonation. Plugs are firing too early. Check the ignition timing. Start with checking points gap, then get a cheap test light and do a static time, and make sure the spark advance is working. Check the plug gap. Get the timing right, and it will wake right up.

 

[Nessism]

So aftermarket exhaust? Is so, I'd move the main jets up a size, or two, and see if the noise goes away.

 

[Atlas]

Ed, it's a stock exhaust (thanks to coastiepete) so my jets should be good, sorry for not mentioning that, and I'll give what you said a try FLHGSRay, I did put new plugs in it so I'll check the gap, it's a 1980 gs so it has the transistorized ignition but I'll still check the timing, I didn't mess with the timing end of the bike, but maybe the PO didn't have it set right. I'm hoping that's all it is. Thanks guys

 

[Nessism]

When you rebuilt the carbs did you verify all the jets are stock? I mention this because many people install "carb kits" which contain crappy aftermarket jets which many times don't match the originals as supplied by Suzuki/Mikuni.

 

[Big T]

Most likely causes of your problem

1. Leaky O rings at head
2. Leaky intake boots
3. Improperly jetted carbs

 

[Atlas]

Big T how can I tell if it is the headers leaking? I don't want to over torque the studs to much , I didn't change the jets , my mistake^o , I did a rebuild but didn't change the jets but I did clean them. I did replace the float valves and seats though and all of the seals. My rebuild kits were made by Tour Max , made in Japan. As far as I know everything in the carbs were stock befoer I took them apart and I didn't mess with the air mixture or change the jets. Big T how do you suggest that I seal the headers at the heads ? Can I use the high heat sealant ?

Sorry for taking so long to respond back , Long days right now. I really appreciate your input

 

[1948man]

The jets should have a number on them. Might take a magnifying glass to read the numbers. I even had main jets marked 115 that turned out to have a bigger orifice than some 150's I had. Turns out the previous owner had drilled out the 115's to about 160.

 

[Big T]

Sorry, not on the exhaust -you'd hear a leak there

I was referring to the O ring between the intake boot and the head, but your 750 doesn't have one.

So, replace the intake boots and any of the clamps that may be bent

You did clean the carbs per the tutorial?

Detonation is a sign of lean mixture

If you replaced the exhaust,you did out in new exhaust gaskets, used antiseize and torqued to spec? (just asking)

 

[Atlas]

I didn't use exhaust gaskets, I didn't know that there were any, when I took the old exhaust off I didn't see any. Do you mean the gaskets down underneath where #'s 2 and 3 cylinder header pipes merge and clamp to #'s 1 and 4? I know that there is one at each joint there. If you mean gaskets at the head/header pipes then no there aren't any there. But it almost sounds like that's where the leak is coming from a header exhaust leak. I'll check the torque on those nuts. (I put a stud and nut system in to replace the bolts that were there and the 5 bolts that had to be drilled out). I've been a bit overly cautious about torquing them down to tight , and I just have the old style torque wrench that isn't all that accurate. The noise seems to be coming from the front of the engine at #4 cylinder and like I had mentioned earlier just on acceleration or under a load going up an incline. I might try to post a sound clip in the next few days and see if it can be heard clear enough to tell from that.
Thanks again

 

[Big T]

No, I mean the ones that go in the exhaust port

1st, check to be sure those gaskets aren't just packed so hard into the port that you can't hardlly see them. Order up some new ones, I'm sure that will cure your problem

Torque? You did download your free factory service manual that includes torque specifications?

so,

New exhaust gaskets
New intake manifolds
New intake clamps?

2 hours work

Hmm, you never did say whether you cleaned the carbs per the tutorial with new O rings

 

[Atlas]

Big T , yes new O rings in carbs , I have a shop manual for the bike so I have the torque specs , I'll check to see if the gaskets are packed in too tight , and order new ones if they are. It could be that the new/ old exhaust that I put on the bike from coastiepete just fits a little different than the originals and that may have something to do with it. The intakes and clamps are all really good, they go tight and seem to work well. One thing that could be replaced maybe is the air filter , the seal around it is a little sub-par. I haven't had the time to check these things yet but will keep you posted. Thanks again

 

[Atlas]

Just ordered some orings for the exhaust headers, it looks like that was possibly the problem because I notice a bit of carbon deposit/blow-by around the one exhaust port . I'll let you know.

 

[Big T]

Yeah, those exhaust gaskets are actually a one use item

People reuse them and they won't crush anymore and seal up the exhaust properly

We'll blame it all on CoastiePete, since he doesn't post here much

 

[1948man]

Did you determine that the gaskets were in place? If they're old you'd swear they're not there when they actually are. They are tough copper gaskets that compress up pretty hard and dark. You have to dig them out with a small screw driver or pick.

 

[Atlas]

1948man, I did get the old ones out and yes they were imbedded in there pretty good , I've finally had time to put the new O-rings in and test drive it. I still get what sounds like valve clatter only on acceleration.So it's back to the drawing board, I think it could possibly be just that ; noisy exhaust valve/s. They could be worn I guess. I have set them and then reset them to no avail . It seems to run okay though , I may just have to bring it in and have it diagnosed by the experts. Hate doing it though , it's soooo expensive , I think around $95/hr , maybe I'll get an after hours motorcycle mechanic to look at it out of his own garage , they are much cheaper.

 

[ddaniels]

The description of your problem fits exactly to the same noise I have in my '81 1000G, and I have not been able to diagnose it either. One of those weird things I guess. I hate the noise as it makes the bike sound like a pile of junk when I take off. But once I'm above about 3500 rpm it goes away.

 

[waltfen]

Yep, I've got same noise on my 81 1000G. I've tried everything, only makes the noise when the bikes hot and under load. Doesn't sound like "pinking", bike pulls like a train and noise disappears about 3000 rpm.