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AltaKnight

AltaKnight

Jedi Knight
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I'm breaking in the new TH5 cam from BPNW c/w new lifters and shortened pushrods because I had the head machined 100 thou to 9.0:1 CR.
The idle is very uneven and lumpy and I have to keep it around 1000 to 1100rpm or else it stalls. It also has a heck of a run-on when I shut off the ignition which I attribute to the raised CR, I have to stall it to shut down.
The engine pulls VERY well once it gets past idle and I'm having a tough time keeping the rpm down during break in. The temp is perfect at 1/4 and the oil pressure is perfect. I checked the plugs after a 40 mile run and they're a very nice tan color. I've got the ignition timing about right so it doesn't pink. I'm burning Shell Silver gasoline (the middle one)
My worry is that I didn't get the cam timed properly and it might be off a tooth one way or the other.
Any thoughts out there?
 
Graham,

We both have similar setups. My idle indicates that the cam is not stock, but does not have your issues. I have it set at between 850 and 900 RPM and it's a little lumpy, but never stalls or runs on. I don't care what anyone says, you should NEVER have to shut any engine down by stalling it. No engine is designed to be treated that way. Let's diagnose and fix the problem.

Where is your ignition timing set? It sounds too far advanced to me. Do you have your vacuum retard connected?

Also, you may have a vacuum leak and with the timing advanced, you could have a rich condition with the carbs masked over by the leak and neither is good for your engine. Hence the tan plugs, but you cheated to get them that way.

Let's start with ignition timing AFTER finding that vacuum leak.

Do you have a vacuum gauge? If you have an issue with valve timing or valve adjustment, that will tell the tale.

Check this site out:

https://www.users.bigpond.com/ergoff/vac1.htm

Two pages of examples in there, with actual gauge movements and readings to go by.

Keep me posted. I'll be on again in the morning.

Good luck......
 
Sorry Don. I forgot that it was night time when I looked at the clock.
 
This morning was play time for an hour or so. I disconnected and plugged the vacuum retard and set my timing at 10-12 BTDC at 850-900RPMS. I got rid of the infernal exhaust popping on deceleration and have a nice smooth pull from 1,200 rpm in third gear. The strong pulling was never a problem, but that backfiring really annoyed me. Having a little burble when backing off is one thing, this wasn't right.

I believe that your comment about bringing the idle down during break in is related to a potential vacuum leak and timing.
 
PB,

In the "old days" we did a lot of diagnosing with a vacuum gauge. It was one of the most used tools in any mechanics box, especially if you did any amount of tune ups.

That's why I enjoy playing with these cars so much.
 
Paul, seems like a lot of savvy mechanics both pros and shadetree are hip to that gauge.
I was fortunate at one time to have an XK-150, that the PO, a very savvy guy, had installed one of those big ole vacuum gauges on the dash. You know the kind with the colored dial, economy, power etc.
At the time I thought it was the product of his idiosyncrasies. I was facinated by it, although I didn't have a clue what it all meant.
 
That's why I put the link there. For those who are not familiar with them, it doesn't make a lot of sense until you see an illustration. If it helps just one person save time, headaches or money, it's worth it.

Kind of like explaining how a dwell meter works with externally adjustable GM points.

Now I am showing my age......
 
Just got home now after spending some "quality" business time in Calgary, 3 hours South on the highway so I've not had a chance to look at anything yet.
I do have a vacuum gauge but didn't check it yet. There could be a leak but I sort of doubt it but it's worth checking that first.
I'm think my timing is about right, it's pretty close to where it was before the modifications which is 8deg BTDC on the timing light WITH the retard connected; it jumps a way more advanced if I pull the hose off with the light attached.
Will report once I've got the vacuum gauge readings.
 
Brosky said:
Kind of like explaining how a dwell meter works with externally adjustable GM points.

Now I am showing my age......
Click to expand...

I loved those things. Sure beat the heck out of everything when I tuned up the family's Impala
 
Oooh,ooh, or using the dwell meter to adjust GM carburetors in the late 70's early 80's...
 
RonMacPherson said:
Oooh,ooh, or using the dwell meter to adjust GM carburetors in the late 70's early 80's...
Click to expand...
Yeah, that was an amusing one ! Had one of those on my wife's 80 Chevy.
 
As a kid (long ago) I often used a vacuum gauge as a diagnostic aid.
My understanding now, however, is that a more-radical-than- stock cam will give a considerably lower idle reading than depicted in that link. I'm not knocking the link; I think the info there can be quite helpful. But if you're running a hot street cam you can't expect to get 17-21 in Hg at idle. My Isky cam, with triple ZS typically gives around 8-10" Hg at idle. Would look similar to what the link depicts as "Late Valve Timing".

Tom
 
8 FI'ers

And what are you still doing up Alan. your turn for the little one?
 
Tom,

I agree with your analysis of the hotter cam, hg readings. I placed the link since the balance of people are closer to stock engines that the one in question.

I also had good intentions to warm mine up and get some readings to give to Graham for comparison, since we're very close in configurations, but I've been traveling and have not driven the TR6 since I posted that link.

I will get them up by tomorrow evening to see how they match up with your readings and to compare to Graham's.
 
So I got back to the garage this morning and plugged in the vac gauge, here's what I've got with an operating temp engine and a 1000rpm idle adjusted for sea level it's reading 11-14" vacuum oscilating about 3", no apparent vacuum leaks that I can locate.
Sure looks like the late valve timing depicted on that web site.
Paul, I would sure like to know your readings.
 
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