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View Full Version : Help needed - got compression & spark, but no go.



El Dopa
13th March 2006, 19:53
What is wrong with my P.O.S bike? Answers on a post (card).

The front cylinder isn't firing.

I got the carbs off at the w/e, and cleaned them up as best I could - took the float bowls off and blew a bit of air back through them. That's about as far as I want to disassemble them without expert mechanical help on hand. There was fuel in both of the float bowls, so I assume the carbs aren't blocked. Is this a fair assumption?

Took the spark plug on the front cylinder out - plenty of spark. Held my thumb over the hole and turned the engine - plenty of compression.

But....The front cylinder still isn't firing.

So what's wrong? I suspect there's a block in the system somewhere, as there doesn't seem to be any fuel getting into the cylinder. At least, there wasn't any splashing out when I span the starter with the plug out.

So, would this be the carbs, or something downstream of them? If it's downstream of the carbs, what could it be, and how do I fix it?

Stopper Dan
13th March 2006, 19:58
sounds like a fuel/carb problem to me if you got spark and compression must be fuel/air (carb) check the jets. some help i hope.

Ixion
13th March 2006, 21:52
Remove front carb. Stick your hand over the inlet. Spin the motor. Still got a hand? If answer's no, you've got suction. Remove your hand from round the inlet valves. Remove plug. Spin engine a few times (carb off). Replace carb, replace plug, leave plug cap off. Spin the engine. Remove plug,is it wet and smells of petrol. No , carb is blocked OR you've got an air leak in the inlet manifold OR a fuel blockage.Yes, something mechnanical - slipped timing something wierd.Take the airbox off, repaet the thing with the hand. If it doesn't suck your hand in, there's an airleak.

BUT: Have you replaced the plugs. Yes I know you've got a spark and the plugs look good. But have you replaced them?

SwanTiger
13th March 2006, 21:59
I don't think you are kicking the bike in fits of rage correctly.

My GN ceased when some bolts came undone and got caught up in the gearbox. My friend and I removed the shredded bolt(s) and replaced the gaskets with maori style newspaper ones.

It worked a treat. Engine blew about 2 months later. Best 2 months of our lives. $800 dollars in fines later. Still best 2 months.

But thats irrelevant, I think Ixion has hit this one on the head.

If you are getting fuel through, then your coil might be fucked or the sparkplug may need replacing. If you aren't getting fuel through, if you have twin carbs, try switching them around and see if you get a different result. If so, then seen as so your not too keen on stripping it, take the carb into an expert for repairs.

Lazy7
13th March 2006, 23:03
fuel tap turned on?

fuel filter blocked? does it have a fuel filter?

tank full of water?

vacum leak somewhere in one of the fuel lines or a gasket between the carb and head?

have you actually taken the plug out, still connected to the lead and held it against the head to see the spark?

El Dopa
14th March 2006, 19:25
Thanks everyone, especially Ixion.


fuel tap turned on?

Yes


have you actually taken the plug out, still connected to the lead and held it against the head to see the spark?

Yes. Well, frame, actually.


tank full of water?

No. Tank is fresh on, with fresh fuel.


vacum leak somewhere in one of the fuel lines or a gasket between the carb and head?


fuel filter blocked? does it have a fuel filter?

Uh, dunno. how do I check?

El Dopa
14th March 2006, 19:29
I don't think you are kicking the bike in fits of rage correctly.



I'm one step away from hulking out on it. I just bought a 12lb sledge for some work I'm doing in the house. It might be cathartic to introduce them to each other.

skidMark
14th March 2006, 19:47
mate where in auckland are you ill come over tonight depending where you are. this thing has been taunting you for months.

pm me your address mate

SwanTiger
14th March 2006, 19:59
mate where in auckland are you ill come over tonight depending where you are. this thing has been taunting you for months.

pm me your address mate

Don't do it!

Its easier to sell your soul to the devil.

skidMark
14th March 2006, 20:04
smart ass get your butt in the chat room so i can hand you the jandel

Lazy7
15th March 2006, 16:52
the easiest way to check for vacum leaks on a carbed engine is to get yourself a can of "engine start" its an aerosol alcohol based product that you spray around the various areas. *normally* you would have the engine running, and if the revs increase, it means that the aerosol is getting sucked into the engine, through a vacum leak and ignites... kinda the same effect you would get from "blipping" the throttle.

but if the engines not running or wont start, that plan probably wont work...

unless its a really big vacum leak and then you could try and run the engine purley on engine start! :crazy:

have you tried filling up the float bowls with gas and trying to start it that way?

if you turn the bike over, is gas getting through to the float bowls?

El Dopa
15th March 2006, 20:33
have you tried filling up the float bowls with gas and trying to start it that way?

if you turn the bike over, is gas getting through to the float bowls?

I assume so. When I took them off, there was a bit of petrol sloshing about in the bottom of them, so I'm assuming that it is getting through to them.

skidMark
15th March 2006, 21:30
solved it..... i think....it will be your spark plug....

spark plugs can have a huge spark but then once in the motor under compression will not spark properly.....

buy a new plug and it will fix your problem....trust me ;)

if you want to confirm it you could always just swap the plugs over

nadroj
15th March 2006, 22:02
If the plugs wet got to be the plug. If the plugs dry got to be a blocked fuel line / jet.

FROSTY
16th March 2006, 00:50
fuel in the sump again??---blocked inlet valve in the carby--if ya still sti=uck gimme a holla--bring the carbs to the yard