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Car stutters under load, revs freely otherwise
hiwex - 25/8/14 at 09:24 AM

Hi All,
I have a set-up with an ST170 engine running GSXR750 ITB's and Megasquirt MS3X. I built the care car a few years ago and has been sprinting and hill climbing just fine until recently, when it's started running rough. When I either try to accelerate from low revs or just accelerate hard to move the VVT cam, it stutters almost as if it's misfiring, sometime also popping in the filter? I've checked the map and all looks OK, so I'm struggling with a diagnosis. Any ideas?
Cheers
Mike

mcerd1 - 25/8/14 at 09:47 AM

how are you controlling the VVT ?

(its been discussed to death before: http://www.locostbuilders.co.uk/viewthread.php?tid=165372 )

[Edited on 25/8/2014 by mcerd1]

britishtrident - 25/8/14 at 09:54 AM

Coil pack & plugs ?

Slimy38 - 25/8/14 at 10:47 AM

quote:
Originally posted by britishtrident
Coil pack & plugs ?


Plugs would be my first thought as well, the stuttering under load is what my bike does when the plugs are reaching end of life. Interestingly when I take them out there are no visible signs of wear, but new plugs stops the stuttering.

ian locostzx9rc2 - 25/8/14 at 10:47 AM

Coil pack and leads and plugs first if they haven't been changed in a few years.

Dingz - 25/8/14 at 11:07 AM

fuel filter, or restriction somwhere?

hiwex - 25/8/14 at 11:38 AM

Thanks all, I'll change the plugs and leads first then, then coil pack and then I'll look at the fuelling, I've got a gauge so should be able to see the pressure.
Thanks a lot all for your suggestions.
Cheers
Mike

hiwex - 24/9/14 at 02:47 PM

Just to update you all and thank you for your help.
It was the coil pack, but I changed the plugs and leads too, found some rainwater around the plugs while at it too.
Problem fixed, raced the next day, came home with trophies!
Cheers all!
Mike

prawnabie - 24/9/14 at 05:44 PM

The rainwater may not be rainwater..... There are 1 or 2 core plugs in-between the plugs that are fairly common to leak coolant.

hiwex - 24/9/14 at 06:12 PM

Thanks, I did check that, all is oK. A Morgan has a louvred bonnet, it's a common problem.
I've got hold of some exhaust heat shield that I'll modify to cover the rocker cover.
I appreciate the thought though.
Cheers
Mike