Random loss of power and backfire

[Shaunb]

I had my engine stripped and new cylinder heads fitted as old ones were cracked last autumn. Not sure if that is relevant but lately I can start no problem , idles fine and drives perfect for about 10 mile, then suddenly be a loss of power, engine does not cut out as the bus suddenly lurched forward as power comes back as I have accelerator pressed then dies again then comes back with occasional backfire. I can stop for 10 mins start up no problem then drive normal again. I have stock engine with oil bath air filter. The only thing done recently when engine was stripped down was I had upgrade to alternator and new fuel pump fitted.
Any ideas much appreciated.
Shaun


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[StuF]

Try a known good coil - sounds like its breaking down when it get hot

 

[TheHewsonFamily]

+1 for coil.

If that doesn't work check fuel pump, fuel regulator (if fitted) and fuel filter to make sure they aren't blocked in any way.

 

[Shaunb]

Cheers guys, don't know if relevant but I use to have fuel level in my filter and now it's completely full of fuel . Will change my coil, and see how it goes.


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[vinvan]

do you have an aftermarket air filter if so it could be your carb freezing, dont know alot about the subject, so it's worth a search on the forum just to check it out

 

[Shaunb]

I have original air filter fitted, I have searched for similar on here and read a little on it, but this is so intermittent rather than all the time , it's scary, just waiting for it to happen, don't dare take kids out in bus now, had it happen on dual carriage way, and bus just slows lurches forward slows and so on, scared my 3 year old.


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[StuF]

If it runs and revs fine when cold or warming up and then once hot starts to kangaroo, backfire and buck down the road I would be almost certain its the coil
My old MK2 used to do it about 15 mins into a journey, had to stop for 20 mins let the engine cool down and drive away - until it heated up again!
Was a little scary doing 70 mph and it happening - almost like the car had the hiccups of indigestion
Nice fresh coil sorted the issue and the car was perfect afterwards

Let us know how you get on

 

[Shaunb]

Thanks Stu, I have ordered a new coil from c and c, they did the beru one which I read was best one to get


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[Shaunb]

Update... New coil fitted still the same. Had a mate look at it and agree it's definitely electrical, going to change my dizzy back to points and remove the electronic ignition to elimate that.


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[Shaunb]

Following on from this issue, I noticed my auto choke and thought could this be the culprit. The marks don't line up so is it possibly ruining too rich or lean?

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[Bluesnailman]

With the engine cooling so will the coil within the choke. When you restart, the auto choke will be activated and will take a few minutes to warm up. It seems to be around this time that you're having problems, just the engine, coil and carb have got to operating temp. I wonder if the choke is masking other problems (like you've got dirt in an air passage in the carb?). For example, with the choke activated (as when cold) the idle circuit is kind of cheated into being only secondary. When warm you need you jets and passages to be completely clear

 

[Mk1jim18]

Hi Shaunb,

I've been having the exact same problem as you in my bay! was driving me crazy! sounded like a shotgun was being fired from the bus!

i had aftermarket air filter fitted so changed that back to oil bath one still nothing...

i had a vacuum advance dizzy fitted a while back had been fine until the problem occurred so thought id change back to the original Bosch 009 dizzy and fitted new points and condenser while out, plus new plugs and leads

now runs absolutely perfect taken her on some good long runs and no problems at all now (touch wood)

Hope this helps

Jim

 

[Shaunb]

Thanks Jim
That's my plans now, going to change out plugs and leads, and put points and condenser dizzy in and take out the electronic points.


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[svman730]

I had a similar problem last year and turned out to be intermitant fuel starvation caused my a in line filter hiding above my gear box. Previous owner had fitted it and I didn't even know it was there. Drained my tank and replaced the filter as well as all the fuel lines and no more bunny hoping for me.

 

[Shaunb]

I've had my fuel tank emptied and changed my fuel filter, but still the same. I've had my carb of and cleaned as much as I can without an air compressor so I can't guarantee its not that, perhaps it needs setting up properly. I'm just going to change my plugs and leads and dizzy and see if it sorts it. Gonna be a few weeks though as I'm away for a while.


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[westy1]

Check your valve clearance could be closing up