4K Stumbling Hesitation

[rebuilder86]

So i posted a topic about a sever hesitation when cold for my GFs dad, and now i am having my own hesitation problems with my 4K.

setup:

4k with dished pistons,

functioning 3k carb (fully functioning, accel pump, idles goood, no leaks)

correct long reach plugs, (one of which is missing a bit of insulator near the wire connection, but has never presented an issue and another which is reading significantly less resistance from the tip to the connection than the other and is also providing a less bright spark than the others when crank testing)

cheap silicone HT leads

5k electronic dizzy

fuelmiser ignition coil to suit said dizzy

 

description of problem

At rest, standing by the engine, engine at operating temp, turning the throttle by hand in one constant smooth motion from idle (600 rpm) up to 2000 rpm in about 1.5 seconds, at about the 1200 rpm mark there is a small but noticeable stumble. I guess kinda like only one cylinder is skipping one beat (perhaps that shitty spark plug).

 

How can this be at this exact rpm with no load, perhaps a spark plug is indeed just shit and at that condition, the stars align and the wave of pressure is high enough and the condition of the mix is rich enough to put out the spark??

I will find the spark plug with the lower resistance and come back to you all with the outcome.

[Banjo]

Hi Jeremy,

Almost certain your issue is ignition break-down somewhere. Repeat the exercise you describe, but do it in the dark at night. If there is a HV break-down in leads,spark plugs, or dizzy cap, you will see it clearly.

 

Let us know how you go.

 

Cheers Banjo

[rebuilder86]

hey banjo, long time no seak!

i haven't had a chance to do anything yet, but that is exactly what i plan to do tonight.

Interestingly, on the way across the island to the city yesterday, i had 2 cut outs, where we were driving up a steep hill for over a minute with 70 % power at about 30 kph, and it died.

Now i am suspicious this is an unrelated issue with fuel supply, it seemed like the bowl was getting emptied before the electronic fuel pump could fill it. let it sit for a minute then started off again and it did it one more time on the climb, but then never again and it was fine. My fuel pump is located in the engine bay which is probably a bad idea for an electronic piston plunger pump.

The whole way back it felt a little lumpy at idle, and a little jerky , like the power isn't smooth.

IS there any way you couldnt see it at night, even with misty water sprayed over everything?

liek perhaps if it is somehow arching from the rotor cap down to the dizzy body inside the cap??

[rebuilder86]

no sparks at all coming from anywhere, checkd at night, with water all over everything.

Seems to be magically running a bit smoother now, I'm goign to guess the fuelmiser ignition coil is not correct for this engine.

The spark plugs are resistor type, perhaps that ʞ©$ɟs up the coil.

[Banjo]

Hi Jeremy,

I'm assuming that you have removed the mechanical fuel pump, & have blanked off the hole in the block. If you have fitted an electric pump, then it is advisable to fit it at the rear of the vehicle, close to the fuel tank, so that the suction distance to the tank is short, & the long run up to the engine & carby is under pressure, rather than vacuum. Just make sure that you current fuel line does have any leaks on the suction side back to the tank, where it could be sucking in air. Also make sure that your fuel tank is venting properly, in case it is building up a vacuum, working against your electric fuel pump. A good indication of tank venting issues, is to note whether there is any inrush air noise when you remove the fuel tank lid, when filling up with a low tank level. Some of the early Rollas just vented the tank into the chassis rail. Later models vented back into the air filter, via a line with a little in-line 1 way valve just near the steering box. It is a plastic valve which is easy to remove & test carefully with your mouth.

 

HV arching inside the dizzy is still visible in total darkness, dispite the dizzy cap being opaque. However, arching inside the cap, is usually clearly visible by removing the cap & carefully inspecting.

 

If they have arched inside the cap for some time, then the only fix is to replace the cap. You can clean them up, but they also seem to track again.

 

Also make sure one or two of your spark plugs don't have very large gaps. This will cause breakdown, when the engine is under load, & the HV takes the shortest path to ground or chassis.

 

Hope that assists, & let us know how you go.

 

Cheers Banjo

Edited March 5, 2017 by Banjo

[rebuilder86]

Yeh i saw 0 arching anywhere, and inside of cap is clean .

i think ive found a potential problem.. no 2 spark plug is weaker than the rest when testing it straight from the main high tension lead. (bypassing the dizzy)

However now I'm suspecting a sticking valve, as the stumble off idle is happening only off idle and i can hear it in the intake, i will tyr upload a video of the sound. you will LOL at my setup.

 

RE, fuel pump, there is no way to blank off the hole properly with the fabrication skills available nearby, without it leaking like a seive, so the old pump is just attached with the arm ground off!! hahah JUNGLE styles.

I was always planning on sticking the fuel pump back near the tank but too lazy and put it off until your wise words just egged me on.

Ive always wanted it up in the engine bay away from water level, because ive had to replace one of the exact type before from crossing the river and water gets into the housing because its not a good seal coz its shit coz everything is shit in this country. I paid about the equivalent of 30 AU dollars for it and they re for sale on ebay for 15. Anyhow, that being said, I did make a waterproof case for it out of a wafer stick container.

YES a plastic tube that you buy chocolate wafer sticks in haha

Maybe if i just transfer that to the rear in that "WATERPROOF" case ill be ok going up long steep hills. Its also hot here so the road is ʞ©$ɟing hot so the fuel lien under vacuum would get ʞ©$ɟing hot which would further increase the risk of air bubbles.

 

anywya a video of the sound is about to be posted stay tuned.

[rebuilder86]

there it is

[Banjo]

Hi Jeremy,

I listened to your utube video & I can hear what you are talking about, the second time you rev the engine up. Could well be a sticking valve. You could try to unstick it, by using one of those additives you put in your fuel, or it maybe it's time for the head to come off.

 

The blanking plate for the mechanical fuel pump hole in the block is not hard. I just used an old flange off a mechanical fuel pump, to mark an outline on a piece of steel. Then cut & filed it, until it looks good, drill two holes & you are there. Just use a fuel pump gasket to seal the joint to the block, or use the plate shape you have cut & filed, as a template on a piece of gasket paper.

 

 

Cheers Banjo

[rebuilder86]

Did you go out of yoru way to take a photo of that and then add the arrow for ME???

well, after my trip to the shops juts now, I'm just about fed up hahah. the thought of moving fuel pumps, covering holes, is just so far away now.... read on to see why

I bought 4 new NGK long projections, which didnt fix the stumbling issue, I'm almost certain its a sticking valve. but it did make things a bit smoother.....

Until i pulled out of the shops and there was an almighty grinding noise when i accelerated, now the ʞ©$ɟING TRANSMISSION IS ʞ©$ɟED!

Clutch in it goes away

if i'm insanely lucky its just a damaged throw out and or spigot bearing, but I'm not an idiot and i know how throw out bearings work, they make noise clutch when pressed in and they are engaged and working, (USUALLY) not when accelerating in gear

ʞ©$ɟ cars.

[Banjo]

Nope ! Its a photo I took some time ago.

 

Cheers Banjo