mighty boy wont start need help

[me217]

hey

sorry about the long one but theres a summary at the bottom.

i got a problem with my mighty boy, it hasnt run in about 6 months because it wont. one day when i was driving it it started coughing and running like crap. as i came out a drive thru. and i just made it back to my girlfriends and it spent the night and went home on a trailer the next day.

that morning i went to try and start it at her place to drive it onto the trailer but it wouldnt start. it sounded like it was fighting the timing. fiddled with the timing at the dizzy, it would spin then but still wouldnt start, had a new fuel filter in the car so we put that in, still no go. so up on the trailer it went and we took it home.

then a week or so later we got time to look at it and we fiddled with the timing again and still nutting so we pulled the timing cover off and checked it on that to make sure it hadnt jumped a tooth and it looked like it had so we adjusted it to suit and put it all back together and went to try and start it and then during the winding we burnt out the starter motor and starter and solenoid are dead so we took one off a f5a we had lying around but it only had a single wire coming out the solenoid instead of 2 like the original one had. still wouldnt start

a while after that we went to have another look at it and replace all the rubber fuel lines as the fuel filter was half full of air at all times, now its full but the engine still wont run. also replaced the points and condenser,

bought a 2nd hand carby off a running f8b and fitted that and it still wont run, and today we checked the timing again and its spot on. and we went to start it today and it would fire but die straight away and would never stay running so im running out of ideas.

summary

fixed timing
new carby
new fuel lines
new coil
new fuel filter
new spark plugs
new fuel pump
new timing belt(damaged the old one)


i was thinking the only thing left could be the fact that we swapped the starters the 2nd wire isnt connected to anything and thats the only thing that i can think of.

[Brayden]

When you say "it won't start" you need to be a bit more specific. Does it crank at all, or is it just not firing? Does it sputter or just wind over on the starter?

Have you done a compression test?

[me217]

it winds but it wont fire and if it does it just fires and dies, it has run one or 2 times but its very rough and its only for a couple secs.

[EVL_801]

I have a similar problem i had the new f5a in my boy working now it decidly wont work it cranks and wants to go but doesnt quite get there, what should the timing be at and is there anything i may have connected incorrectly that may be the cause for this issue?

[Brayden]

I noticed you said the timing belt was damaged. How did that happen?

[me217]

well we had the big washer thing that holds it on the pulley on the wrong side so the belt was rubbing on the timing case. so i decided to chuck a new one on just to be sure.

[Brayden]

Okay, I just thought that it might have been stripped at some point.

I would be doing a compression test before anything else, just to see if the problem is mechanical or electrical.

[me217]

compression is all even around the 120 mark. low i no but it was running.

[gadj]

Had same with my F8b - Double check timing belt (found mine 2 teeth out)
also have a good look at timing marks on flywheel (I had been timing up on the wrong mark until I found several marks existed - I found TDC using screwdriver to feel piston crown on No.1 with both valves closed - then looked for 10degree mark)

[ToranaGuy]

Does the engine have the correct flywheel for it? The timing marks on the F5a & F8b are a fair ways apart if you have both flywheels to compare them.

I had all hell trying to time my F8b with a F5a flywheel, using the timing marks. When i decided to rip off the rocker cover, pull #1 plug & do as gadj suggested to find #1 TDC, i then managed to get it timed fairly quickly.

Also, you know you can pull a spark plug & earth it on the engine, get someone to crank the car & check for a spark at the end of the plug. If you have spark, you can then try & drop some petrol, kero or so on down the carby & give it a try.....

Cheers

ToranaGuy

[me217]

Does the engine have the correct flywheel for it? The timing marks on the F5a & F8b are a fair ways apart if you have both flywheels to compare them.

I had all hell trying to time my F8b with a F5a flywheel, using the timing marks. When i decided to rip off the rocker cover, pull #1 plug & do as gadj suggested to find #1 TDC, i then managed to get it timed fairly quickly.

Also, you know you can pull a spark plug & earth it on the engine, get someone to crank the car & check for a spark at the end of the plug. If you have spark, you can then try & drop some petrol, kero or so on down the carby & give it a try.....

Cheers

ToranaGuy

we timed it up with the rocker cover off and i've tried start ya bastard(fitting name) and it didnt change it at all. and we checked the spark plugs getting spark and it is.

it sorta coughs spins over for about 2 revs on its own and dies.

[ToranaGuy]

That's a weird one then, isn't it?

120psi per pot is the bottom end of serviceable iirc. My current F8b that's in pieces was 150/120/145 from 1-3, and is really a pig to start, probably due to crappy compression. I've got it timed correctly, carby rebuilt, coil, leads & so on replaced, only reason it's so hard to start could be the compression.

I'm starting to think if that 120 is in each pot, you might be SOL ($hit outta luck) and need to find out why comp is so low, is it rings or valves causing it?

Cheers

ToranaGuy

[me217]

im guessing the compression is so low cause its had a hard life. thrashed around the road my a friend of the family then sold on to someone then we bought it off them as a bush basher thrashed it around the farm for a year or so. then put it in the mighty boy when i got it.

so it could be time for a rebuild?

[Brayden]

If you're getting 120 across all cylinder then I'd be doing a leakdown test to see if the cause of the problem is worn rings or because the valves aren't sealing properly - which would indicate a cam timing issue.

It is unusual for worn rings to give consistently low results across all cylinders.

[me217]

how do u do a leak down test?