Yet another DuneRunner :)

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at least a third one because I can access the filter just fine and I moved the throttle linkage below the servo horn so my clearance is just fine :) I was under the impression that the 1" velocity stack offers better air flow to the engine and I was wondering if the streadstack has the same advantage.
 
Quick question for you guys: is it normal for the idle rpm to go up and down? When I first start the engine and it's cold, it seems to idle higher. As I drive it, the idle rpm goes down a bit. First I thought it's just the normal behaviour as the engine gets hot. However, it sometimes idles fine while being hot, then 3 minutes later it idles so low that it's almost dying. I then give the idle screw a full clockwise turn and it's fine. Then 3 minutes later, the idle is high again and I turn the idle screw back to get the nice smooth idle I want. Is this normal or is there something I'm missing? A couple of points I already checked:

  • quickly slamming on the throttle from idle there is no bogging down, so I don't think the LSN is too rich
  • it's not a tank venting issue, opening the gas cap has no effect on rpm.
 
It could be an air leak. With the engine running you can spray some carb cleaner on the intake manifold. If there is a leak the carb cleaner will get sucked in and fluctuate the idle speed.
 
The stock intake manifold has been known to develop leaks. There are aftermarket aluminum ones available which hold up better.
 
I actually already have the aftermarket manifold, just didn't get around to installing it yet
 
I'm planning on changing both the carb and the intake manifold sometime this week, hopefully that will fix it. I'll also try your suggestion Rob with marking the idle screw.
 
I went out again today... the idle rpm thing didn't happen again, but I cannot get it started while hot if my life depended on it. When it's cold it starts the exact same way each and every time (pops on the 3rd pull with the choke on, then starts up at the 3rd pull with choke off). After running it and leaving it for 5 minutes, it will not start, no matter what. I tried with choke, without choke, while holding WOT, without WOT... nothing. It will not start until it stays for a few hours. This is really annoying... :(

I also noticed my exhaust is leaking (there is oil coming out from between the engine and the black exhaust box), could that have anything to do with it?
 
From what I've seen here on the forum it's a common problem so someone should have an answer.

It's not something that's happened to me though (fingers crossed)
 
heres a guess at why this happens, i can remember a few of these same situations the carb is not letting fuel pass. something to do with carb make up. the weak tabs on carb parts are pushed closed by the heat coming from the case thru pulse channel, which normally pulls the fuels.

its a limitation of carb (stock). the hi performance carbs don't seem to have same issues.

thats a guess, truly think its a stock carb problem where low duty parts placed in hi stress duty situation just can't keep stable positions , small tabs, thin diaphrams, pins closures under stress won't work right...as the motor is running the fuel is "COOLING" all these parts , when its stops temp will spike and pinch close.

compression falling off would be the next concern. if compression is weak and runs fine first couple mins , then starts to fade a bit , thats definite compression problem. and with heat and part growth it all grows apart and there is no compression.
 
the car runs just fine until I turn it off, so I don't think (and hope :D ) it's a compression issue. It actually seems to run A LOT better when hot, I suppose that's normal, I usually let it idle for about a minute after starting it the 1st time and then drive it slowish for another 2-3 minutes. During that time, the car is running better and better and I think it "peaks" after 3-4 minutes. After reaching that peak, there is no drop in performance no matter how long I run it, just the annoying issue of restarting it after turning it off. I'm now even refueling it with the engine running to avoid not being able to restart it, it's not ideal...

I'll install most of my upgrades during the next few days (intake manifold, wt-1107 carb, jetpro exhaust, 8k rpm clutch, new CMR7H spark plug (i initially bought the iridium CMR7HIX but it doesn't fit)), all those new parts should cover pretty much all possible problems you guys listed, so... I'm hoping for all the problems to magically disappear after the upgrades :) Fingers crossed...
 
i think as the stock carbs age with use(30+hours) they loose their performance pretty quick. and eventually become untunable and won't hold a tune at all.

the iridium plug is tall won't work with the cage if i remember right.
 
The car has only about 3.5L of fuel through it, it would be pretty weird for the stock carb to be that short-lived...

phreerider said:
the iridium plug is tall won't work with the cage if i remember right.
Click to expand...
Exactly :(
 
just a weak carb with limits.

if any adjustments maybe LSN a fraction richer, may have clogs at needle end (hence the varying idle) close all the way and reset where you want it, it will push away small debris trapped at needle end. thats part of my practice to CLEAR needle seats when things start wondering
 
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