5k High Rpm Misfires!

[seabiscuit]

Hi everybody.

 

Have got my 5K in KE70 and it has been misfiring in in high RPM's, more so when the driveline is under load.

I have played around with the timing to see if it was that, but can't seem to find a sweet spot. So wondering what

other issues may be causing this to happen. Could it be carby? Motor is a worked 5k with 35/75 Cam, ported head,

solid lifters and probably lightened flywheel (I didn't build motor) with a 32/36 weber bolted to the top. 160/165 air

jets, unsure on fuel jets. Any help would be greatly appreciated!

 

Cheers,

Vince.

[KENut]

Leads shorting out maybe? I've seen engines where the leads weren't only shorting out across each other, but they were also arcing across to the extractors beneath them. Lightnings in the engines bay! Was happening at higher rpm, maybe because the leads couldn't support that much current.

[seabiscuit]

Leads shorting out maybe? I've seen engines where the leads weren't only shorting out across each other, but they were also arcing across to the extractors beneath them. Lightnings in the engines bay! Was happening at higher rpm, maybe because the leads couldn't support that much current.

I've got 9mm top-gun leads... Don't think they can't handle the current. I do have a shitty old Coil, though. Still should be able to hold the spark though.

My friend says it could be the spark-plug gaps. I didn't set them when I put them in, but would it make that much difference?

[KENut]

Top Gun isn't that great, no offence. But yeah, they really should be good enough. Dunno bout the spark plugs, pull them out, thouroughly check for cracks and look at the colour etc, clean and gap them chuck them back in. Maybe you should try swapping the coil for another one.

[coln72]

Had issues with after market leads on my first 5k. Replaced them with factory leads and misfire disappeared.

[seabiscuit]

Had issues with after market leads on my first 5k. Replaced them with factory leads and misfire disappeared.

Did yours misfire only when you wanted to go fast? (High RPM)

 

Just another quick Q. Where do people get Toyota replacement gear?! Especially stuff like leads, oil/fuel/air filters etc!

Do I have to get it from a Toyota dealer?

[muzke30]

I use repco and rare spares down hear, have u checked the timing mate i had similar problem with my ke30 used timing gun worked a treat neva ran so good b4 also distruibtor cap could need changing any crack? hows the points?

[seabiscuit]

I use repco and rare spares down hear, have u checked the timing mate i had similar problem with my ke30 used timing gun worked a treat neva ran so good b4 also distruibtor cap could need changing any crack? hows the points?

Swapped over the distributor cap to one I had on my 4k and problem is still there. I'll try and play around with the timing a little more (with a timing light this time)

and see if I can't overcome the problem.

 

As for the leads issue I swapped leads over to stock 4k items and problem was still there, checked the gap in the spark plugs, tried swapping coils, played a little with carby

mixture screw etc. still doesn't like being rev'd! :bash:

 

I'm in the process of fully rebuilding another 32/36 Weber to put on there just so I can rule it out. It couldn't be anything to do with the carby though, could it? If I leave it

at a constant flow of petrol and wait for motor to rev up it still starts doing it (at same acceleration rate).

[muzke30]

id say have to be something with spark for it to back firing while ur driving. try using timing gun see how u go.

 

question does the car back off revs wise is u keep pushing it and it back fires? may indicate is not getting enough fuel at high revs

[seabiscuit]

id say have to be something with spark for it to back firing while ur driving. try using timing gun see how u go.

 

question does the car back off revs wise is u keep pushing it and it back fires? may indicate is not getting enough fuel at high revs

I'm sorry.. But I didn't understand that :(

 

Carby fully cleaned and is now airing out. Might have some time tomorrow morning to slap it back together or tonight if I feel keen enough.

2'ish weeks flipping around with this car is getting on my nerves! :P

Edited August 25, 2009 by seabiscuit

[muzke30]

sorry way to tired and not explaining my self properly

 

what i was trying to say is if ur pushing it wen gets to high revs does it struggle or do revs go down prior to back firing

[seabiscuit]

sorry way to tired and not explaining my self properly

 

what i was trying to say is if ur pushing it wen gets to high revs does it struggle or do revs go down prior to back firing

The revs go down due to the misfiring.. If it weren't misfiring, the revs shouldn't go down for any reason. If they were

I would be worried that I'm not in Kansas anymore. I'm not saying that the revs would keep climbing, but they should

max out and keep firing at a constant RPM!

 

What are you trying to work out? :P It doesn't struggle to get to the revs, but when it gets to higher revs it misfires...

That's all there is to it.

[philbey]

have you had the carby jetted and tuned?

[seabiscuit]

have you had the carby jetted and tuned?

I haven't... The previous owner would have probably had the carby jetted. It's probably moderately to highly untuned now since I've owned it.

I don't see how the carby could cause a misfire, though... Especially if I leave it at the same amount of throttle and wait for the rev's to rise.

By all means correct me if I am wrong! What is there to tune apart from air/fuel mixture and idle screw (not that idle screw is really "tuning")

on a 32/36 DGV carb?

[beerhead]

Might be worth checking the plugs-

High revs can cause spark plugs to have there spark blown out if the gap is too wide.

 

I've got 9mm top-gun leads... Don't think they can't handle the current. I do have a shitty old Coil, though. Still should be able to hold the spark though.

My friend says it could be the spark-plug gaps. I didn't set them when I put them in, but would it make that much difference?