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advice please - L18 jerking/hesitation


zed

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I have an L18 with Nikki carb. Can I get some suggestions please - I have to travel a long distance tomorrow, with a trailer, and I can't find the problem. My diagnostic skills are weak - although I did re-build this motor myself.

Symptoms: engine starts & idles perfectly. It will also rev perfectly in neutral (no load). As soon as I accelerate on the road, it jerks/hesitates, then surges - can't even do 50mph on a level, uphill it's worse. It started quite suddenly while I was travelling on the highway on my last trip a few days ago.

I've changed the fuel filters - run two of them. Changed the plugs, points and condensor. The carb fuel level is right on the line in the sight glass - so I'm assuming fuel is not the problem? Any advice would be much appreciated - thanks

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Hesitation when an engine is put under a load, especially when acceleration, often is a sigh of a weak ignition system.  With points, the gap, or dwell is critical.  If the gap is too large, the points are not closed long enough for the magnetic field in the coil to build.  if the points are too close, they do not open far enough, and some spark energy is wasted by sparking at the points, instead of the spark plug.  used points need to be set by the dwell, an electric measure of the point gap.

Other causes of a weak spark could be a poor connection somewhere in the ignition wiring, or the whole secondary wiring in the ignition system could be bad.  (cap, rotor, plug wires, coil to distributor lead)  if you have not changed spark plugs in a while, that could be an issue.  The recommended interval for spark plug replacement on a 521/L16 I think is every 12,000 miles.

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The above plus look for a loose wire to the ignition system. Engine under load moves more and a loose wire is like turning the key off and on.

 

The carb may be full if it sat idling before you check. Next time you are out, floor it until is hesitates and as quick as possible (and safely) get it out of gear and the key OFF. This will preserve the condition of the carb fuel bowl. Now take a look mat the fuel level. Your description sounds like it's running out of gas too

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was the coil changed???????????? hot low ohm coil will burn or arch out the points.

if electric ignition forget above post

 

soemtimes the bushing wears out on these and causes point bounce.might even affect the electric did on mine at high rpm and was rotor wiggle

 

 

main fuel jet is plugged.

 

does it run better is Choke is ON(cold elctric choke) or pulled(manual choke) if yes then gas is going thru the 2nd barrel main jet

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thankyou for all this advice. 

I took the air cleaner off, looked down the carb: with the engine idling, there is fuel flowing in one 'throat' - as it should be. When I open the throttle wide, fuel only flows in the second 'throat' for a few seconds, then stops. Note - This is not the accelerator pump - the accelerator pump tube runs into the first (primary?) 'throat' - it's working fine as far as I can see. With the throttle wide open, should there be a constant flow of fuel in the second 'throat'? The fuel level stays constant in the sight glass even when I rev the motor and 'choke' it with my hand over the intake - so fuel flow seems ok?

I've re-set the points, put yet another new condensor on, removed and cleaned, gapped the plugs, checked valve clearances, cleaned inside the dizzy cap, checked plug wires with ohm meter - all good. Vac advance is working. Am going to try again...

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you can get the motor raised up in rpms then stick a screw driver to hold open the 2nd barrel(if this is a stock vacuum 2ndary carb). then out your hand over the main barrel to keep the air moving in the 2nd side of carb to keep it running.

 

 

like I said earlier ck the dist shaft for bushing wear. side to side wiggle on the shaft. Most time this will act like a bad condensor and carb will pop and back fire.

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