Carb to PI conversion

[Mark Ogram]

Hi all,

Apologies,I know this topic has been covered several times on the forum, but I am at my wits end.

Purchased a CP car last year that was on SU carbs. I have now converted back to injection. Purchased a "lot" of all the parts needed to do this (all reconditioned and from a TR Register member). Started the car a couple of days ago, it started quickly, but the revs were all over the place, between 1200 and as much as 3000rpm. It seems to have a mind of it's own. Any advice would be most welcome - I just want to get out in the car and drive it before the weather turns.

Thanks.

Mark.

[Waldi]

Hi Mark,

Assuming ignition timing is ok, and all components are in good order, I would start with balancing the TB’s. If there are bo air leaks, the car should stall if the idle air screw is closed. 

Waldi

[Stagpowered]

At a guess the throttles have all been nicely cleaned and as a result they don't seal too well leading to very high idle speeds. (I am assuming they are set up correctly)

I made this mistake when I converted my USA TR6 to injection. I solved the problem by applying a layer of viscous grease to the butterfly seating area. This reduced idle speed to an acceptable level until the normal layer of gunge had accumulated on the inlets after a few thousand miles of use.

When I converted my TR250 to injection using scrapyard PI throttle bodies (this was nearly 30 years ago), I made sure I didn't clean around the butterfly seating area and had far fewer problems.

Neil

[Waldi]

I did clean my CP throttle bodies thoroughly. I was aware of similar experiences like Neil’s from this forum, but did not like the deposits in my TB’s and removed all of it, finished the cleaning of the bores with a alu polishing compound to clear metal. This enabled me to properly align the existing butterflies on new spindles (by sight). Car idles ok, and I can stall it with closing of the idle air valve.

Regards,

Waldi

[Mark Ogram]

On 9/7/2019 at 8:47 AM, Waldi said:

I did clean my CP throttle bodies thoroughly. I was aware of similar experiences like Neil’s from this forum, but did not like the deposits in my TB’s and removed all of it, finished the cleaning of the bores with a alu polishing compound to clear metal. This enabled me to properly align the existing butterflies on new spindles (by sight). Car idles ok, and I can stall it with closing of the idle air valve.

Regards,

Waldi

Thanks Waldi,

Done some more fiddling and idle is now 1050rpm, closing the air screw is still not stalling the engine though.

Regards.

Mark.

[Mark Ogram]

On 9/6/2019 at 8:28 PM, Stagpowered said:

At a guess the throttles have all been nicely cleaned and as a result they don't seal too well leading to very high idle speeds. (I am assuming they are set up correctly)

I made this mistake when I converted my USA TR6 to injection. I solved the problem by applying a layer of viscous grease to the butterfly seating area. This reduced idle speed to an acceptable level until the normal layer of gunge had accumulated on the inlets after a few thousand miles of use.

When I converted my TR250 to injection using scrapyard PI throttle bodies (this was nearly 30 years ago), I made sure I didn't clean around the butterfly seating area and had far fewer problems.

Neil

Hi Neil,

I have done some more adjustments and applied some grease. Engine now idles at around 1050rpm.

Regards.

Mark.

[Mike C]

No other vacuum leaks- brake booster or its vacuum hose?

[Mark Ogram]

1 hour ago, Mike C said:

No other vacuum leaks- brake booster or its vacuum hose?

No other vacuum leaks, just started the engine again and now idling at around 900rpm - going in the right direction, still getting popping and banging from the throttle bodies though.

[Waldi]

Hi Mark,

very good, if you have idle screws on each lever of each TB, I use these for idle adjustment; if you release these screws, AND the 3 rods are “free”, i.e. not pulling on the lever, the butterflies should fully close. Check each of the 6 ports with air flow meter. If one is much higher than the rest, the butterfly disk may not be seating properly.

I have set idle rpm and idle synchro with these 3 screws, and am aware others do not use them. I do this because these 3 screws are the most direct way to adjust the butterflies. If you would do this with the 3 rods, as some others prefer, temperature variations in the 3 rods (from exhaust radiation) will give variation in idle and synchronisation. But make up your own mind (that’s what I did).

Regards,

Waldi