21 replies to this topic

[Pauly]

Hi all,

Got a little niggle with my new engine. When the revs drop below 2,000 rpm it seems to judder and buck.

It doesn't happen when your on the thottle, only when I take my foot off the throttle and the revs drop down, would it be a timing issue? Set at 6-8 degrees at the moment and I have a lucas 65dm4 dizzy which has been re-curved (no vacuum advance, going to re-fit it soon).

The engine pulls like a train and theres nothing else out of place with its running, its just this niggle.

Quick little engine spec.

1310cc
Kent 276 cam
SRE fast road head
Standard bottom end (balanaced)
Med pre-verto ultralight flywheel/clutch assembly
Standard metro helical cut gearbox, with minispares x-pin diff
S/C drop gears (1:1 ratio)

Thanks guys.

[POWER5LAVE]

hi mate im not going to be able to help but i can give you some advice from my own experiences. mine was also juddering but it was when you hit 2,500. spent an afternoon with a timing gun found it to be out by miles set it correctly juddering went away. i did have to change my plugs aswell as the twin sparks werent working good enough or were faulty when i brought them but fitted some trio(think thats what there called) and it seemed to help with it.

and im running a 998 with a stage 3 head.

[Pauly]

Hmm, ive got a feeling its timing.

Anyone with any other things it could be?

Is 8 degrees the figure to go for? Or should I set it at 12? Its running 10.5:1 compression with bp ultimate fuel.

[Carlzilla]

i think you should give me the engine mate, then the problems will go away


and did you have fun fighting the torque steer wednesday?

edit:

just had a thought, mark it, adjust the timing at idle (possibly backed off?) and see if the lumpyness goes, then leave it at that and see if the vac advance sorts out the rest of it

aint got a clue when it comes to stuff like this really though paul, might work though? wont hurt to try

Edited by Carlzilla, 23 July 2010 - 06:18 PM.

[Pauly]

That wasn't torque steer mate, it was me trying not to hit the central reservation .

Think it will benifit from being advanced, to maybe 12 degrees?

Just would like to know what a safe limit is for timing, with the compression ratio, I dont want to run into deternation issues. Hard to hear any pinking over the sound of s/c drop gears .

[Turbo Nick]

pop round tomorrow if you want chap, we can have a play with the timing and use my calibrated ear for pinking, lol.

[Pigeonto]

[quote name='Pauly' date='Jul 22 2010, 08:19 PM' post='1888381']
Hi all,

Got a little niggle with my new engine. When the revs drop below 2,000 rpm it seems to judder and buck.

I'm vey glad to hear that(meant in the nicest possible way) as I have the same and am glad I'm not alone. I am worried when you say on your new engine as I have given up on this one and am building another,hoping not to have this happening.This is a "slave" engine from a metro 63hp.The bores were suspect butit has 160 to 140 compressions so not awful.I went daft with the porting(it has the big 35.6 inlets as std) and thought it was the prob so changed to a MG metro head and left it well alone.Didnt help.Have had engine out and tried 3 different cams! to no avail,544,731,stdmetro. Tried with and without my 1.5 rockers on all cams( I have a heap of old head and rocker gaskets). What I do know is its WORSE with the 1.5s but Im not changing it anymore.I started to think that as I set 10.75 CR the bores being bad were letting it past and causing some sort of imbalance but it doesnt have crankcase compression.Its better with a 38 carb than the std 44 it had.The worst rpm is when it hits1800 as you are decelerating,will need another new top steady soon! but not accelerating.Its lovely and powerful 2200 up.(731,roller rockers,LCB and 1 3/4 system,44 carb,light f'wheel) Tried all sorts needles.Sorry to go on but any suggestions would help me ,especially as you have done your engine and have this still,very concerning.Tried timing all places but needs ALOT of advance to norm.....Any of this familiar?

[turbominicooper]

i too am having this problem, ive got a standard 1275 with built carb and am getting this juddering crap below 2500.

i ahve rtied endless variations of things:

timing set.
mixture adjusted.
tried various needles some of which help and some which ruin it.
thought it may of been head gasket so changed that.
useed stage 3 and standrad head.. saem thing happens.
tried splitfire and ngk plus.
sport and standard coil.
wiring is how should be.
battery warning light visible.
earth strap strong.
air filter clean.
tried 2 carns old and rebuilt - same issue!

what the funk is happening here?

[turbominicooper]

i too am having this problem, ive got a standard 1275 with built carb and am getting this juddering crap below 2500.

i ahve rtied endless variations of things:

timing set.
mixture adjusted.
tried various needles some of which help and some which ruin it.
thought it may of been head gasket so changed that.
useed stage 3 and standrad head.. saem thing happens.
tried splitfire and ngk plus.
sport and standard coil.
wiring is how should be.
battery warning light visible.
earth strap strong.
air filter clean.
tried 2 carns old and rebuilt - same issue!

what the funk is happening here?

also changed fuel line
added regulator and return line
checked fuel filter -ok

[Pigeonto]

i too am having this problem, ive got a standard 1275 with built carb and am getting this juddering crap below 2500.

i ahve rtied endless variations of things:

timing set.
mixture adjusted.
tried various needles some of which help and some which ruin it.
thought it may of been head gasket so changed that.
useed stage 3 and standrad head.. saem thing happens.
tried splitfire and ngk plus.
sport and standard coil.
wiring is how should be.
battery warning light visible.
earth strap strong.
air filter clean.
tried 2 carns old and rebuilt - same issue!

what the funk is happening here?

Think we best start a club.Yep forgot to mention,tried 2 different coils,different dizzy(both 65DM4s).Thought maybe water getting in through a crack in inlet ports,no.Maybe some oil getting up past rings? I cant see why happens on low revs with throttle shut,surely the timing and fuel mix dont apply as its virtually taking nothing in to be at the wrong mix or for the timing to affect.Almost wish I'd left the damn thing with its dismal 50 hp engine in,only done 30000, but it doesnt half go when it wants with this engine in, 55 hp ATW

Edited by PIGEONTO, 23 July 2010 - 09:29 PM.

[Carlzilla]

pop round tomorrow if you want chap, we can have a play with the timing and use my calibrated ear for pinking, lol.

dont suppose you want to do my brakes for me too do you nick?
im terrible with listening to stuff, i have to get others to faf with my timing and stuff.

That wasn't torque steer mate, it was me trying not to hit the central reservation .

LOL, did you decide last minute you were going to turn right?

[turbominicooper]

its just giving me a headache.

spending all day at work tryin to figure out what it is, lyin in bed tryin to figure it out, doggy wit the missus tryin to figure it out - absolute headache!

[Pigeonto]

its just giving me a headache.

spending all day at work tryin to figure out what it is, lyin in bed tryin to figure it out, doggy wit the missus tryin to figure it out - absolute headache!

If the one I'm now building does it,its going in the village pond. Think I'm now off to do as you-lay in bed wondering what it is.3 of us now, hope some one else reads and has had-and resolved-this

[turbominicooper]

ive got another mini sitting in my garage so might use the carb and ignition parts off that in hope it cures this

[Turbo Nick]

pop round tomorrow if you want chap, we can have a play with the timing and use my calibrated ear for pinking, lol.

dont suppose you want to do my brakes for me too do you nick?

put your callipers on the right way round first