Not pulling through 5K RPM

[chickenstock10k]

I spent the last couple of weekends outfitting a new petronix ignitor II distributor and a set of headers RD Enterprises. After setting the timing, resetting the idle adjusting the carb balance and topping up the oil I popped out for a test drive. It sounds great and pulls hard but it seems to run out of steam at around 5K RPM. It pulls hard through 5K and then just seems to run out of steam. It doesn?t misfire it just doesn?t want to pull.

Timing is set to 10ish degrees at idle.

I?m going to check the plugs and replace the fuel filter but aside from an issue with the distributor, I?m not sure what it could be. Any thoughts on trouble shooting would be welcome!

[chickenstock10k]

Well, I think I found part of the problem... fouled up plugs. Swapped out plugs and it seemed to help out quite a bit. Not 100% but it helped.

Now to figure out why everything seems to be running richer...

[jono]

My engine had the same symptoms with cam timing retarded by 5 degrees.

Great to around 5k rpm then did not want to rev much further.

I corrected the cam timing and it would now rev to destruction if I let it. Lost a bit of grunt further down however.

In hindsight the retarded timing was perhaps better for all round driveability - more torque where needed.

Perhaps worth a check?

Jon

[gjz30075]

Did it pull beyond 5K before the distributor change? What's total timing and at what rpm?

[chickenstock10k]

Is it possible that the chain could have jumped a gear? I pulled the cam cover and the timing chain tension seemed right it did not confirm the cam timing. It did feel like it pulled further before the header / ignition swap.

There is around 12ish degrees at idle and while I thought the Ignitor II has 24 degrees of advance I only saw 30ish degrees of total advance when I put the light on it. I had replace d the federal emissions vacuum retard distributor that the previous own had been using where they had something like 20 degrees of static and a total of 30+ of total advance. I think they were trying to compensate for the fact that the vacuum retard dizzy has very little advance.

I got a few backfires through the carb when I was initially setting the timing. Maybe I damaged the carbs somehow?

[chickenstock10k]

One thing I?d add is that it feels really good up to around 5k where it just falls off quickly. No misfire, It just doesn?t keep pulling hard. Looking around for twin cam torque curves it seem like max power is right around 5.5k. Perhaps with a little less timing I?m running into the stock power band? This is my first lotus and a relatively new project so I?m not totally sure what to expect at times.

[69S4]

I had a similar experience when I replaced the original 23 series distributor for one of the 43D's - it was all the suppliers had at the time. The car ran fine but lacked top end.

Years later ( ) I checked the bob weights and found they were marked as 7 degree ones. A quick check with a strobe light confirmed it with only 14 crankshaft degrees of advance showing up. That plus the 9 degree static advance (Stromberg) was just 23 in total versus the 33 it should have had. I modified them to give 12 degrees and the car has been much more lively. I've no idea what advance characteristics the springs are giving but the car does pull a lot better over 4k revs for the extra advance.

[chickenstock10k]

Alright, update from the +2 garage.

I double checked the timing, adding a little advance and then set it back to where it was. Advance was set correctly.

Plugs were a bit sooty but after an extended run on the highway all was right as rain.

I figured it was time to run a compression test to make sure all was well. Motor was cold but I found 120 across all cylinders. A little lighter than I would like but at least it was consistent.

Next, valve cover off and a fresh investigation begins. It looks like the timing is off by a tooth and my guess is the problem and may be linked to both the lower compression and lack of performance. I am still struggling to wrap my head around how the chain would jump a tooth...

I think the next step is to remove the cams and re-time the valvetrain.

[2cams70]

Can't you just put the old distributor back in temporarily and see how it goes?? You can't rely on compression gauges. If the reading is consistent across cylinders that's good. If it's low consistently it could mean many things and not necessarily that there's something wrong with the engine.

[chickenstock10k]

I could pop in the old distributor but now I?m concerned that the cam timing isn?t set right!

[Chrispy]

Should be able to check valve timing pretty quickly with the cam cover off. Line the little lines up and see how it looks

[JJDraper]

[quote="I think the next step is to remove the cams and re-time the valvetrain.[/quote]

Not sure why you need to remove the cams to re-time the valve train. Find out which cam if off by a tooth and move the appropriate cog (check at TDC). If you need to change valve clearances, yes, but cam timing should not involve removing them.. Slacken off the cam chain as much as possible, give a hefty push down on the chain between the cams, making it slack and you may even be able to jump the chain a tooth without disturbing the cogs. I have been out by a tooth before, and the symptoms are as you describe.

Jeremy

[chickenstock10k]

I got the timing cover off, sorry if you couldn't see the photo I uploaded and one of the cams is certainly off by a tooth. Perhaps I was being a little over the top suggesting that I remove the cams to adjust the timing on the valve train.

I guess I am just having a hard time visualizing how I slacken the chain enough to adjust only one cam without disturbing the crank and losing TDC.

[nmauduit]

I got the timing cover off, sorry if you couldn't see the photo I uploaded and one of the cams is certainly off by a tooth. Perhaps I was being a little over the top suggesting that I remove the cams to adjust the timing on the valve train.

I guess I am just having a hard time visualizing how I slacken the chain enough to adjust only one cam without disturbing the crank and losing TDC.

it can be easier than it seems to let a tooth slip when the chain is slackened when fiddling with the crank and individual cam pulleys... while at it you may want to double check TDC is still on the crank pulley mark, so as to be sure that you start on a well known base.

[69S4]

If there's a bit of wear in the chain you can certainly 'walk' the chain round a tooth as Jeremy suggests. You just have to work out which side of the cam you need the slack in order to move the cam the correct way. Remove the tensioner to gain maximum chain slack. A new chain may not have enough 'give' in it so you'll have to remove the sprocket, turn the cam and put it back on. Don't drop the bits down the hole No need to remove the cam.

When I time my cams via the sprocket marks they don't line up exactly at tdc (about 1/2 tooth's worth out) so I guess I need some offset dowels. If one tooth out gives the flat above 5k characteristic under discussion would correcting my 1/2 tooth error make any noticeable difference? Anyone got before and after experience?