Strange engine noise ?

[catdna]

Well, I think it's from the engine - hard to tell as it only happens when in motion.

The issue is this - on my trike, at around 60mph with little or no throttle I get a horrendous 'clattering' noise, give the throttle a tiny twist and it vanishes - only ever happens at that speed, usually in top gear.

Now, as my carbs are knackered (broken mixture screw stuck in the carbs), I wondered if it could be the engine over compensating at certain revs one affected cylinders (and as it happens with no / little revs, I guess that 'jet' would affect it at that speed).

Haven't had a chance yet to put my *new* set of carbs on (no broken mixture screws ! hurray !) to test this theory - but I wondered if anyone else had any ideas ?

With the rocker cover off, everything looks sparkly-new - shims are all fine, oil seems fine, it's just this odd / loud noise at around 60mph in 5th that sounds horrible

Cheers
Chris

[MindWebs]

the info you seek is yours for the taking...

If you look in the repair section of this site you will find a page describing
the methods used for removing those broken pilot needle screws
(i think that's what your actually talking about)

it didn't seem like it was too complicated, just takes time and care.
It would be MUCH cheaper then new carbs..

it your baby, Good Luck!!

Webs

Also, yes it can cause some problems of running lean if the needles are blocking the pilot holes, be careful, may damage engine if it's too lean.

[catdna]

If you look in the repair section of this site you will find a page describing
the methods used for removing those broken pilot needle screws
(i think that's what your actually talking about)

it didn't seem like it was too complicated, just takes time and care.
It would be MUCH cheaper then new carbs..

it your baby, Good Luck!!

Webs

Also, yes it can cause some problems of running lean if the needles are blocking the pilot holes, be careful, may damage engine if it's too lean.

We've managed to remove the needles already - although the holes might be a bit 'bigger' now :-(

I managed to get a half-decent set of carbs from ebay yesterday (half decent in that, only 2 mixture screws were broken off - the other 2 were fine and no signs of 'drilling') - so we have enough now to make a new set.

It's just the weird noise that's worrying me - can't really describe it, and probably couldn't record it (too much wind noise I guess). I'm hoping it'll go away once the newly assembled carbs are put on.

The trike has barely been ridden (already knew it was running lean) because of the carb / lean issues and needing to upgrade the brakes - they're sorted now, as shown by the big rubber skidmarks down the road where we tested them :-)

Cheers
Chris

[DGXSER]

I'm no expert, however, in my opinion, a noise that is that speed specific, and gear specific as you describe it, would be transmission and drive line oriented.

The engine (although the tranny is in the engine on these machines) could care less what speed your going unless your REALLY lugging it by making it pull form say 1k rpm in 5th gear up a hill, it changes with revs. So an engine noise that was rev specific would occur whenever you hit that rev, no matter the gear. JMHO

[Crazcnuk]

What rpm are you doing at ~60mph?

Being a trike, I don't know if your different than the bikes.

These bikes had a detonation issue at 3500-4000 rpm, on some models.

[catdna]

What rpm are you doing at ~60mph?

Being a trike, I don't know if your different than the bikes.

These bikes had a detonation issue at 3500-4000 rpm, on some models.

I've no idea on the RPM at 60mph - we never managed to get the digital speedo to work properly with the coils - it always shows between 1 and 2k.

At a guess, I'd say around 4000rpm (the trike weighs about 450kilos, so it's going to rev / strain a bit more than the standard bike).

So what's the detonation issue exactly ? and is there anything that can be done about it ?

Cheers
Chris

[tarzan]

The vacuum advance will cause that.Yamaha had a different advance as a fix back in the day.Some guys have adjusted the timing a couple degrees with some success.Some guys have disabled the vacuum side of the advance.
Most guys just learn to live with it.I wasnt able to get my special to eliminate the knock.

[Crazcnuk]

Tarzan covered it.

Yamaha says it is not a destructive detonation, and will cause no issues. They offered the modified vacuum advance for those that insisted it be 'fixed', but it was not covered by warranty, the owner had to pay for the fix.

You can try and run a tank of premium in it, just to see if it goes away.

[b.walker5]

..You can try and run a tank of premium in it, just to see if it goes away.

That solved my detonation problem, and it's worth a try. I went from 91 octane to 95 and never heard the noise again. Got better MPG as well. I was worried about overheating due to higher combustion temps and pressures but we live in a cooler climate down here, not unlike the UK but not as wet, and it hasnt been an issue. I occasionally run 98 octane as well and it goes like a scalded dog, but it runs a lot hotter.

Just a thought though, It could be a timing or primary chain rattle. Try running at no load in lower gear or in neutral. Normally you be under acceleration in lower gears and any slack on chains is taken up, so it wouldnt be apparent until unloaded (cruising) in top cog.

[catdna]

Thanks guys - I'll try the higher octane method, and the lower revs / gear too when I get the trike back this week (fingers crossed !)

Cheers
Chris

[catdna]

SOLVED !

After an age of rebuilding carbs from 3 different sets, we got the trike going again, only to be faced with the same horrible noise, but this time at much lower revs / gearing.

After propping the trike up and giving it a good thrashing, turns out the prop shaft was slightly 'bent' (and getting worse) - a new one was fabricated and the noise has now vanished !

Should be getting the trike back this weekend - can't wait !

Cheers all
Chris