hard knocking on take-off on first gear

[Baitweller]

Need a little help please, 1983 Aspy. Just got it back on the road with all maintenance completed (bought it as a running project bike). Runs real strong once it get going. Shifts good through all gears and rpm's are great. The problem is getting off a dead stop in first gear. The engine knocks hard like I'm taking off in 3rd or 4th gear??? The more gas I give it the worse the knocking. I have to ease the clutch out while giving it light throttle to keep the knocking down. Any ideas on what causes this? If it was a car I would guess some kind of malfunction with the vacuum advance (my guess and maybe not even a good one at that). Other that that issue the bike runs good. Someone told me to add Octane Booster but I'm using high-test gas at 92 oct. now. I adjusted the valves, new timing belts, new plugs, new fuel pump, original plug wires (?). Any comments are greatly appreciated.

Thank you AGAIN for all your help.
MV

[Aussie81Interstate]

You will need to synch your carburettors, that is what is causing the knocking - they sound like a bucket of bolts if not done correctly.

[WingAdmin]

What he said. Unsynchronized carbs cause unbalanced power pulses, causing the primary chain to rattle loudly, and the more load you put on the bike, the worse it is, particularly at low RPMs.

Large primary chain

Read up on the process here: viewtopic.php?f=11&t=81

[dingdong]

Also you don't need to use 92 octane gas. Your bike will like 87 octane better. That is what it was designed to use.

[Baitweller]

You guys are amazing! This stuff comes so easy and its second nature to you but for people like me who end up with problems way over their heads, this web site is a life (and wallet) saver. Can't thank you enough for the quick response and on-point solution. I've ordered my 4-gauge vacuum kit and all the fittings in the "how-to" article. I'm confident I can do this with the clear instructions and photos provided.

Thank you,
Manny

[Aussie81Interstate]

When using the vacuum gauges, make sure you sync all the gauges first - to the one cylinder - I think #3 is the best one to do this on - as it is non adjustable - with all gauges set up to read the same (if brand new gauges they should probably be pretty accurate).

Then when you do link them all up to the individual carbs then you can adjust each bank 1& 3 then 2 & 4 then bank 1 with bank 2.

You will notice when doing this you will be adjusting the idle several times..

Make sure the gauge needles are not fluctuating wildly by adjusting the small damper screws..

Lots of videos on you tube covering synching 4 cylinder motorbikes.

here is an example - not a bad video either



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[Baitweller]

Aussie, quick question. I received my vacuum gauges and completed the procedure as required. The bike sounds amazing. Problem is when I start tightening the lock nuts around the 8mm adjustment screws it throws the sync way out again. I'm making sure to keep the screws in their position but once I start tightening the sync falls off? What do think causes this.
Thank you

[Aussie81Interstate]

When you lean on the screwdriver or lock nut you are subconsciously tightening your grip, even leaning on the screwdriver will get things out of whack. Just try and be gentle to the stage of getting the nuts firmed up - it will take some patience.

When firmed up just one drop of thread locker on the head of the screw will stop them moving.

Good job..

[WingAdmin]

Aussie, quick question. I received my vacuum gauges and completed the procedure as required. The bike sounds amazing. Problem is when I start tightening the lock nuts around the 8mm adjustment screws it throws the sync way out again. I'm making sure to keep the screws in their position but once I start tightening the sync falls off? What do think causes this.
Thank you

Yup, just the movement of the locknut on the screw makes enough of a change that it throws it out a bit. You have to just use a bit of trial and error to get it to the point where you have it right with the locknut tight.

[patbrandon1]

Always great info and kind people on this site. Thanks Scott for all you do that makes it happen. Your example of class, kindness, and willingness to share information freely, has made this the quality site it has become.

I do have a question though. How often do people sync their carbs? I'm sure that will vary with people. I synced mine last June, and it still seems fine. No marbles rolling around in the engine. But would doing it again this year make sense?

[WingAdmin]

Always great info and kind people on this site. Thanks Scott for all you do that makes it happen. Your example of class, kindness, and willingness to share information freely, has made this the quality site it has become.

I do have a question though. How often do people sync their carbs? I'm sure that will vary with people. I synced mine last June, and it still seems fine. No marbles rolling around in the engine. But would doing it again this year make sense?

I typically only do mine whenever I feel like it needs it, rather than a set schedule. I've NEVER synced the carbs in my GL1500, as it's always been whisper-smooth.

[Wingsconsin]

Worth doing
My sons 1980 was a beast until we got eh carbs synched properly (which took several trials)
But once it was done -- more power, better MPG , easy cold starts , ran great --
I wish we still had that bike - but he sold it to upgrade to a 1500 ; which he sold and upgraded to an 1800 now --

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