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Zx7r carbs not fuelin enough
po79 - 29/11/12 at 10:16 PM

Hi Guys,

Me again with another problem!!!!

I've got the engine up and running with the megajolt now but kept thinking there was something wrong with the timing as the exhaust manifold kept glowing red (proper glowing!)

However aftewr messing around with everything else I decided to look at the carbs and whilst the engine was running I pulled the choke full on and within a minute the exhaust cooled down and stopped glowing and the car sounded better (although it sounded ok without this).

So clearly she needs more fuel, I've not yet adjusted the mixture screws as time ran out and thought I should ask here first but I'm sure the main jets are number 170 which I believe related to its size in MM?

So they should be 1.7mm which I thought was fine for the Pinto engine?

Should I just adjust the fuel mixture first or does anyone have a better idea of whats the best thing to do?

The engine is a 2.0 Pinto, group one valves, ZX7R carbs and megajolt ignition with a standard bottom end and I think the CR is around 10.1 :1 (approx) so not really high.

Cheers,

Poe.

snapper - 30/11/12 at 07:21 AM

The main jet does its work higher up the rev band
Idle circuit and mid range are a different circuit
Needle height and profile also have a bearing
AFR meter and/or a rolling road set up

deezee - 30/11/12 at 11:23 AM

A 170 jet is'nt 1.7, its the rated fuel flow in ccm per minute. Both ignition advance and fueling affect exhaust temperatures. You might be running too retarded, leaving loads of fuel to continue burning in the exhaust. Also, as mention your jets don't affect idle. That's what the idle circuit is for. What's your afr say?

po79 - 30/11/12 at 04:01 PM

Cheers for the replies guys,

I just checked and Keihin jets are sized by diameter in MM and the jet numbers do correspond to their size in MM so 170 Jets are 1.7mm just if anyone else's info really.

Carbs are not my strong point as you have probably guessed.

I've tried four or more different maps that have been used on other Pintos so the timing shouldn't really be hugely out I only checked and rechecked this cos a car I had years ago did the same thing with the exhaust manifold due to poor timing.

I'm hoping to get a few hours on the car this weekend and I'll make adjustments to the mixtures but I can see to much fuel being the problem given how it reacted with the choke full on its got to be the opposite surely?

I'll see what that does hopefully next week I can get her out on the road and see how she behaves under different driving conditions.

Can anyone recommend a trusted rolling road tuner in Somerset who has experience of bike carbs on road cars as that will be the next step once I've ran the new engine in.

Cheers,

Poe.

mcerd1 - 30/11/12 at 04:51 PM

quote:
Originally posted by po79
I've tried four or more different maps that have been used on other Pintos so the timing shouldn't really be hugely out I only checked and rechecked this cos a car I had years ago did the same thing with the exhaust manifold due to poor timing.

have you checked that TDC is actually were the map thinks it is ?

BaileyPerformance - 30/11/12 at 09:01 PM

quote:
Originally posted by mcerd1
quote:
Originally posted by po79
I've tried four or more different maps that have been used on other Pintos so the timing shouldn't really be hugely out I only checked and rechecked this cos a car I had years ago did the same thing with the exhaust manifold due to poor timing.

have you checked that TDC is actually were the map thinks it is ?


mcerd1 is probably right, you may have your trigger wheel on wrong.

The numbers in the megajolt are meaningless if the wheel and VR sensor are not installed correctly. The VR sensor must be 8 clear teeth ahead of the missing tooth (count 8 teeth) - aligned in the middle of the 9th tooth. (90degrees from center of missing tooth to center or VR)

The VR sensor mounting bracket must be rock solid, ANY movement will effect the timing.

I would not expect the fuelling to be that far out to cause hot manifold, is it lazy to rev up? if so it points to timing.

Just a a rough guide, set the timing in the megajolt as follows (at all loads)

500-800rpm 10deg
1000rpm 12deg
2000rpm 20deg
3000rpm 30deg
4000rpm 34deg
5000-7000rpm 36deg

The above will not cause hot manifold

cal - 1/12/12 at 09:33 PM

Dude, I run zx7 with 160 jets, what have you done with the air correctors?? Also what retardation have you to set?? Sounds very much like running lean/ over retardation I would check your trigger wheel first off. I run a zetec with the same carbs so slightly different

Rob Allison - 2/12/12 at 11:26 PM

If the carbs are the type as in pic then the air corrector, in the top blue circle centre brass hole (think thats right) needs to be blocked off.
Mine ran extreamly lean without it done.

cal - 3/12/12 at 07:04 AM

The post above is correct though it depends what jets are being used , you may have to reduce the air corrector size rather than block it. 160 jets with air correctors blocked works well. , 170 with pin prick air corrector jets also works nicely

po79 - 3/12/12 at 09:02 PM

Cheers for all the replies guys,

Just got back from the car now.

All sorted it was a lean mixture and just needed the air mix screw backed off two more turns.

Like you have all suggested the first places I looked at was timing and the trigger wheel/VR sensor position then the actual megajolt settings I had completely convinced myself last week it couldn't have been the fuel mixture but once I poured more fuel in by having the choke fully out and saw how differently she behaved it seemed the best culprit to investigate next.

Definatly going to double check the air connectors and make sure there isn't any other places air is getting in next time I get back to the car.

Really do appreciate all of your time and input's to help me out, top men!

Poe.

po79 - 7/12/12 at 06:25 PM

Just some info on this.

I checked my air connectors the other night and they were as I remebered (haven't looked at them since I get the carbs 2 years ago!) and they have tiny holes.

I have blocked they off completly but the engine doesn't seem to like it and runs to rich now. I screwed the air mixuter screws in one and half turns and its not so bad bad doesn't seem to run as smooth as before.

MOT on Monday so I'll leave it as it is but I think Cal was right when the said 170 jets run better with a small hole in the air connector.

Cheers for all the help again.

Poe.