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Misfire > 4000 rpm


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My new GT6 engine is still having a few problems bedding in.

After 1500 miles I began to get a clashy clatter at high revs & high rpm - tappet check and change of points since I can now not really get back to testing if the clatter has gone because above 4000 rpm the engine begins to misfire and won't now hardly rev  above 4000 rpm - it becomes rough and increasing misfires.

Not sure where to start - as I'm loathed to make things worse - particularly as below 4k rpm it's very crisp.

Known issue is slight wear on the throttle spindle bushes - can any here suggest a logical sequence of checks - and whether to explore fueling or electrics first.

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Is this happening only when driving, or when stationary? Does it clear as soon as you bring the revs down? Does a bit of choke make any difference?

Could be any number of things but if changing the points caused it to get worse, I'd start by taking off the distributor cap and thoroughly examining everything nearby. Are there any fraying wires that might get earthed when the base plate moves?

If nothing obvious, then maybe swap points & condenser for a known-decent set if available.

I'd also check the manifold nuts are all tight and there aren't any other likely air leaks, apart from the worn throttle spindles. 

Pete

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Good advice from Pete.

Some of questions from me:

Did the misfire exist before the tappet check and points change?

Did the tappet check reveal any big changes needed?

Did it have the head nuts re-torqued / tappers set / oil changed somewhere in the 500 - 1000 miles range?

What cam is fitted?

I suspect that the misfire is points related. As you say it’s still crisp lower down possibly too much gap leading to insufficient dwell to charge the coil, rather than gap closed up.

 I don’t really have an opinion on the noise at this point - curious to see if the tappet adjustments have done the trick.

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tappets set to 0.014" & were all pretty good. Head re torqued & oil changed by TRE @ 500 miles - Cam - a TR Enterprise Special ??? - its a rally / sprint profile and pulls all the way up from 2000k to its now rev limited 4k! ... but was easily pulling to >5k before I meddled ( albeit with the worrying characteristic of the clashy sound so reminiscent of the head that had the springs bore themselves in )   Incidentally I needed to change points as the LT lead got wrapped around the dizzy spindle wedging between the points heel and cam lob snapping off the heel !!! 

Points set at 0.020" ... should I try 15 or 18 thou' ??

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50 minutes ago, Greta said:

ok - shame faced admission time - could the tiny teenie weenie washer beneath the points pivot securing post ... that may have dropped into the dizzy....be fouling the springs or weights???

Haha! Oops...

36 minutes ago, Greta said:

Incidentally I needed to change points as the LT lead got wrapped around the dizzy spindle wedging between the points heel and cam lob snapping off the heel !!! 

Points set at 0.020" ... should I try 15 or 18 thou' ??

Was that the lead from the condenser, or the coil? Was any other damage done in the process, which you might have missed at first?

If it's a Delco dissy make sure the U-shaped LT terminals are making good contact where they slot behind the points spring (if that makes sense!). The fit is usually piss-poor, although less bad with NOS points.

 

 

Edited by PeteStupps
to remove misleading statement about points gap! 
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I think The Golden Spanner award goes to Nick. 

 0.020" if set not quite on the crest of the lobe can easily be 0.025"+  - More accurate setting ... ( must refit one of those solenoids with a button ) with a smaller gap does indeed now allow it to rev to 5000.

although it's much much better it still has difficulty holding 5000 rpm .... Dropping back periodically.

so now that's been understood  perhaps I'll start again & try to refit my luminition ignition kit that TRE disconnected. See if that will facilitate good ignition at even higher revs .....To be continued.

Thanks -  as always to all that offer help.

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  • 1 month later...
On 9/7/2020 at 7:21 PM, DeTRacted said:

Points gap should be 14-16 thou, so yours are a bit wide making the dwell too short. 

Problem solved - twice.
Fairly certain the points gap and perhaps setting them when the heel was just off the crown was the original cause ... although temptation had me fiddling with the timing by twiddling the dizzy and setting by ear ! - thanks. Got everything set up and ran great for c120 miles or so - only to reoccur... doh.
So despite TRE saying they couldn't get my Lumination to work I thought I would try - I  had no trouble reinstating it ( suggests they just wanted to sell me their points set etc ) and now everything seems much crisper and easier to start. - Will keep you all posted - thanks to those that offer advice.

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  • 10 months later...

Ultimately this engine too had to go back to TRE .... several months on & I again have a refreshed car and engine with reground crank. I've lost track of how many engines & returns for further work this car has had ... but the coming weekend I'm eventually back to Rallying - Ilkley Jubilee .... just got to see if the transmission holds up to me having to scream it to get it on the cam.  I'm thinking o/d on 2nd will be necessary in future if I'm to have the tractability I need navigating the country lanes on regularities.

 

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13 hours ago, Greta said:

I'm thinking o/d on 2nd will be necessary in future if I'm to have the tractability I need navigating the country lanes on regularities

You were talking about this mod a while ago weren't you? I've just put overdrive on my spit with it enabled on all forward gears. To be honest it's not really necessary for me with a standard cam and 4.11 diff, but was one of those things I wanted for no particular reason. Plus I didn't have the actuator for the standard inhibitor.

Happy to share circuit diagram and details if you're interested. There was a good write-up of it in the November 2019 Club Triumph magazine as well, from Dirk Devogeleer.

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9 hours ago, PeteStupps said:

 To be honest it's not really necessary for me with a standard cam and 4.11 diff, but was one of those things I wanted for no particular reason.

I find o/d 2nd on my 1147cc 3:89 MKII useful for pulling up hills when 2nd is too low but the car won't pull 3rd. On the GT6 - on trundling regularities at 21 -  26 mph in the back lanes I think o/d 2nd will be perfect between high revving 2nd & bogging in 3rd... anyway we'll see - Mike Papworth is sorting a an additional inhibitor switch for the opposite side of the selector.. Always keen to see others developments if you can share your wiring diagram. - Thanks Pete

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15 hours ago, mpbarrett said:

Why did you have to get engine rebuilt again, was it a a bad grind of the crank?

I was wondering that too......

On the OD and second gear, if you are still running the D-type I'd be a little of using it in second with a tuned 2L (or any 2L).  Ok with the 1200 and the 1300 but pushing the limits beyond that.  Ok for pottering maybe, but welly it and I think it might not be very long-lived.  The 2L ought to be really flexible anyway unless daft cam.....

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39 minutes ago, Nick Jones said:

I was wondering that too......

On the OD and second gear, if you are still running the D-type I'd be a little of using it in second with a tuned 2L (or any 2L).  Ok with the 1200 and the 1300 but pushing the limits beyond that.  Ok for pottering maybe, but welly it and I think it might not be very long-lived.  The 2L ought to be really flexible anyway unless daft cam.....

I don't need to hint much to you guys do I! - Yes poorly ground crank traced eventually to an error with tooling at the machine shop ( credit due thou' all work required to rectify done FOC ) & yes the CAM maybe too "daft" for a road rally car - doesn't begin to pull properly until 2500rpm ... forcing me to work the gears a lot more. TBH I think I preferred the stock CAM for road rallying regularities but I'm looking forward to see if it has it's advantages on longer flowing tests.... because it certainly is punchy at higher rpm.

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23 minutes ago, Greta said:

TBH I think I preferred the stock CAM for road rallying regularities but I'm looking forward to see if it has it's advantages on longer flowing tests.... because it certainly is punchy at higher rpm.

Can relate...... Vitesse cam is a bit too daft really and only road usable because the engine management just about tames it.  With ITBs as well it should be perfect (ish) but would be far simpler just to down-cam a bit.  However..... the way it goes in 3rd gear from about 2,800 upwards..... is strangely addictive :devil:.  My GT6 though with standard Mk2 cam and Strombergs is just lovely low down and actually goes quite well further up too - just 40 hp or so down on the Vitesse....

Hope your engine stays fixed - you are overdue a result on that!  Good to hear it was sorted as warranty.

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Glad you got this sorted and TRE stepped up. 
my “new” engine is as good as ready with them. 
I just need to get my g/box sorted re- worked under warrantee first.

taking it out tonight !

TRE want me to go to their points based dizzy but I think I want the 123 on mine 

it’s not an FIA. Spec so no real need for points. Part of their reasoning is it’s repairable on the side of the road or in paddock 

my reasoning - don’t want to have to repair it.

I use a 35 quid accuspark points replacement unit and it’s been great!!

good luck with the rally let us know how you go on. 
H

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Glad to hear about the engine Greta. And there is always the temptation to run too much cam but it is fun :devil:

@Hamishit is important that points/condenser are repairable at the side of the road because it is something that you WILL need to do.

However my experience with Accuspark in three different cars and many 10s of thousands of miles is that they just work reliably and consistently apparently forever.

I am interested in the second gear OD option for the Spit. I would prefer to go the second inhibitor switch route if anyone had info on that?

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if you have a reversing light switch on the gearbox then this could be used to drive a relay so that the OD is inhibited if the gearbox is reverse.
It would mean that you could use the OD on all gears then, but probably not advised...
On my gearbox I didnt have the plate to hold the inhibit switch so built a support to hold a couple of Micro switches and drive them from a cam attached to the end of the selector rod. The cam is shaped so that it drops out of OD when changing between gears (3 and 4). 
There is also a simple Pic Micro doing all the logic so that I have a push switch to select the OD.

Mike

 

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