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!
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?
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.
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.
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.
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.
[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.
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.
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?
to be on the safe side I would check the workshop manual… the principle is first to find TDC (which may or may not correspond to crank pulley mark at 0), then time exhaust side (which is done with the chain under tension between crankshaft to exhaust sprocket), then to do inlet timing (chain under tension between the 3 sprockets). When I do it, I turn the engine over CW several times to take the slack back (the tensionER being on the inlet side). After valve timing has been duly set and checked and tensioner set back to proper chain tension, the ignition timing needs to be checked, too.
ps: I don’t think a few degrees off alone would be enough to prevent a stock engine in decent condition to free rev above 5k … but it seems there are a few points to check and clear before any further tuning can be attempted.
B Buckland seems to state. Cam lobes on #4 cylinder point toward each other.
I believe light force, forward and backward of cams. Will indicate closed #4 valves because of springs. Though I am not sure if it is that easily noticeable.
As you add tension from the tensioner. The slack must come from somewhere. Most likely intake. Therefore, if You consider one cam to be advanced. One might consider advancing intake as tension will spin intake cam backwards.
It’s pretty easy. Turn the engine over until the crank is at TDC and the two No.4 cam lobes are rocking towards the centre on the lifter. Slacken off the chain tensioner. Remove the crank sprocket on intake cam. Chain will be slack, adjust the cams so the little lines align with the top face of the head. Put the chain back on. Tension it back up and turn it over a few times. You’ll probably have to re-time the distributor.