CR throttle body balancing

[88V8]

poor seals around the injector adaptors. I have thought that they seem a bit loose. Could a poor seal here contribute to the hesitation?

It creates an air leak, so Yes.

 

Ivor

[Peter Cobbold]

When on the PI my take-off manoevre involve blipping the throttle and lifting the clutch foot as the revs dropped in the 'blip', then opening the throttle once clutch fully engaged. I suppose the MU diaphrgam was still in the process of recovering its raised position after the blip when the throttle was opend the second time, giving the extra fuel needed for the load. And now with one SU and the blower I just plant the right foot - but with the clutch already engaged - the carb piston damper does the rest.

 

Its interesting that the Bosch K-jetronic had no provision for acceleration enrichment. Apparently it was not needed because the rise in air flow was being monitored well upstream of the butterflies,by a flap-actuated potentiometer that then signalled to enrich the fuel injection. In contrast the Lucas PI senses air pressure (not flow) after the butterfly and the fuel response is slightly delayed by mechanical inertia in the MU diaphragm and so on, whereas in the K jetronic its electrical and faster. So we could fit a air flow sensor in the plenum and.......... nah, easier to blip the throttle.

[AndrewP]

Hi Quentin,

 

Perhaps crack the butterflys open a little (using the idle screw) and close down the air bleed a little to get a bit of air flowing past the butterflys at idle. This may help reduce that stumble as you wont be snapping the throttles from fully closed to WOT. It also means your not fully shut so potentially 'bruising' the aluminium throttle body.

 

For what its worth though..if you can get it to idle at around 950-1000 rpm, and it accelerates nicely though the revs..go have a beer and enjoy the driving!

 

Cheers

 

Andrew

[Quentin]

 

Fair enough. It does go well now otherwise! You know how it goes though. I'll find something else when I get to bottom of this one . I did actually try leaving them all open a bit (with idle screw closed) and it didn't seem to help which is why an alternate cause for the hesitation has to be a real possibility. Plugs appear good (NGK BP6ES) and I have a new rotor arm (not red one). I DO have mismatched ingnition leads. Two of them are silicon high performance 8mm (on 1 and 2) while the others are whatever came with the car. Would that really generate a problem only from idle though? My plan of action is as follows but not necessarily in this order: 1) fit the extra o rings to the injector adaptors (at least maybe that will mitigate my residual misfiring when cold - which only lasts 20 seconds or so); 2) Try opening butterflies no.5 and no.6 a bit more than no.s 1 through 4 to compensate for any lag on the CR spindle connections (Technicalities CD), 3) get a new full set of ignition leads and 4) possibly richen the mixture a 1/4 turn (with advice). Failing all that maybe try setting up all the TBs to the average of each pair as I mentioned earlier or finally have a go with the dowell!

[stuart]

Get one of Martins (Distributor Doctor) red rotor arms as well.

Stuart.

[Peter Cobbold]

Try a smidgeon of excess fuel just before taking off from tickover. If richening the mixture gets rid of the hesitation you know its from too lean mixture. And can progress from there.

[Quentin]

Ah! damn good idea sir. Will give that a go.

 

PS: Thanks Stuart. Will order one today

Edited June 21, 2011 by Quentin

[smizgals]

...being poor seals around the injector adaptors. I have thought that they seem a bit loose...

 

 

I too have some loose and have wondered if that is a factor in me not being able to stall the engine by shutting off the air bleed.

 

Ivor confirms that creates air leaks. Anyone know a supplier of these?

 

Stan

[Quentin]

I too have some loose and have wondered if that is a factor in me not being able to stall the engine by shutting off the air bleed.

 

Ivor confirms that creates air leaks. Anyone know a supplier of these?

 

Stan

 

 

You can get them from chris Witor. http://www.chriswitor.com/proddetail.php?prod=516922RM

 

However! Mine are brand new from him. They came complete with new "o" rings. As mentioned, my old ones appear to have had two "o" rings on them. Whilst apparently incorrect - as I got a new set of "o" rings also with my new injectors, I figure I will fit them as well and see what happens - unless there is a damn good reason why the second groove should NOT be fitted with an extra "o" ring? Failing that, I could wish for slightly thicker "o" rings.

[88V8]

.... - unless there is a damn good reason why the second groove should NOT be fitted with an extra "o" ring? Failing that, I could wish for slightly thicker "o" rings.

 

Seem to recall reading that it's too hard to get the injectors out.

 

Mine came from Malcolm. I dare say he'll sell you some or tell you where to get the correct size.

 

Ahhhh.. a post by TIMS.... November last year...

 

http://www.altecweb....ubcategory8110a

 

They are Viton.

 

for reference :

 

O-Ring Viton, Imperial (Product Code ORV-BS008) Inside injector

O Ring, Viton, Imperial (Product Code ORV-BS115) Injector to push fit

 

Ivor

[smizgals]

You can get them from chris Witor. http://www.chriswitor.com/proddetail.php?prod=516922RM

 

However! Mine are brand new from him. They came complete with new "o" rings. As mentioned, my old ones appear to have had two "o" rings on them. Whilst apparently incorrect - as I got a new set of "o" rings also with my new injectors, I figure I will fit them as well and see what happens - unless there is a damn good reason why the second groove should NOT be fitted with an extra "o" ring? Failing that, I could wish for slightly thicker "o" rings.

 

 

I just found one here http://www.tr-register.co.uk/forums/index.php?showtopic=26602&st=0&p=192539&hl=orv-bs115&fromsearch=1entry192539 on the forum.

 

ORV-BS209 listed prior to the recommended ORV-BS115, has only a 0.08mm smaller ID and looks as if it can qualify as the oversize one with a 1.74mm larger OD? I don't need 25 though! Want to share?

 

Stan

 

PS Ah..., just saw Ivor got there first.

Edited June 21, 2011 by smizgals

[Quentin]

Sure. First I would just like to check the difference between my current rings, the ones that came with the MU and the old ones! I don't want to buy more of the same! Can I come back to you tomorrow?

Q

[smizgals]

Sure. First I would just like to check the difference between my current rings, the ones that came with the MU and the old ones! I don't want to buy more of the same! Can I come back to you tomorrow?

Q

 

 

OK. If it turns out you need them, then it may be better for you to buy them and post them to me.

 

I ordered 6 x Insulator & O Ring from Chris Witor anyway.

 

Stan

Edited June 21, 2011 by smizgals

[badshead]

PS: Thanks Stuart. Will order one today

 

 

Quentin

 

As the donor I can confirm your rotor arm came from Martin at Distributor Doctor shortly before he began his red period!

 

Bill

[Quentin]

Quentin

 

As the donor I can confirm your rotor arm came from Martin at Distributor Doctor shortly before he began his red period!

 

Bill

 

 

Well, I've ordered the red one now anyway so I can give yours back!

[Quentin]

Update:

Balanced the TBs as best I could but still getting hesitation from idle. Even by closing down the idle screw and balancing the TBs with higher idle, I still get hesitation.

 

All told I have now done the following:

 

Newly Reconditioned MU (K_Raven_Smith)

Newly Reconditions injectors (K_Raven_Smith)

Magnecor blue HT ignition leads;

Red rotor arm

Double o rings on the injector adaptors (more to try and resolve difficult starts from very cold (say after a week) - didn't help;

Fuel Pressure 110 psi

Checked vacuum - about 8 "Hg and I can stall the car from the idle screw (or could when I was balanced with the idle screw)

Reset spark plug gap (plugs are a lovely straw brown - except they were very sooty and slightly damp after some hours playing with the TB balancing and revving the engine - is there a clue there?)

Checked and adjust valve clearances

 

This leaves me with the following:

 

Coil

Distributor

Throttle bodies; and

MU calibrated wrong (my CAM is unknown). It was calibrated for a saloon and therefore expecting CR type vacuum levels. My vacuum is lower than this though I don't know what the CAM is.

 

As I know the TBs are still poor I am going to bite the bullet and get them reconditioned. Meantime when time (and appropriate help) permits, I will have a stab at identifying the CAM.

 

I'll post an update as I progress - unless I get a torrent of requests to let this topic (or saga Ivor ) die off

[Guest ntc]

Are you taking the car to IWE?

[Peter Cobbold]

Quentin,

So putting on a bit of excess fuel has not helped - the hesitation is not due to a 'lean spike' ?

Peter

[Quentin]

Regarding the excess fuel, I never properly tested that. I got sidetracked by the sooty plugs thinking it was over fuelling. In fact I was concerned that it might be seriously over fuelling due to less vacuum ( 8" ) than the MU was set up for (saloon 12") and wondered if that was the problem. However, after a good hard run on sunday I found the plugs all nice and straw brown. So I'm a bit confused..in case you hadn't guessed!

 

I will check tomorrow evening after disconnecting the fast idle.

 

Regarding IWE, I have to confess I haven't been planning to go. I did go to Malvern last year but the thought of a 460 miles round trip up the M5/M1 is not filling me with much enthusiasm. Could wish I didn't have the noisy sports exhaust the PO fitted as well. It's quite wearing on the ears on motorways Might try for a swapsy one day . I haven't ruled it out completely though. In fact the more I think about it........ Meanwhile I am planning to go to the Silverstone Classic the previous weekend though.

[Quentin]

OK Peter, disconnected the fast idle and checked for hesitation with choke. This is what I found. Btw I warmed up the car first. With choke on about 1/3 I can significantly reduce the hesitation. However, the car is really unhappy at this level of choke. Idle is much smoother with no choke. Your thoughts?

[Peter Cobbold]

OK Peter, disconnected the fast idle and checked for hesitation with choke. This is what I found. Btw I warmed up the car first. With choke on about 1/3 I can significantly reduce the hesitation. However, the car is really unhappy at this level of choke. Idle is much smoother with no choke. Your thoughts?

 

Quentin,

Its looking like the richer mixture you provided by the choke is helping abolish the hesitation. That points the finger at the inability of the PI to provide transient enrichment. Note that the enrichment is only needed for maybe 1 to 2 seconds to cover what is known as a 'lean spike' upon take-off. So try pulling on the choke one second before opening the throttle and push it in again a second or two later. If the hesitation goes then we need to look into an alternative strategy to avoid you having to tug on the choke cable on every take-off.

That could be quite simple to do, but lets be sure its a lean spike issue first.

Peter

[AndrewP]

Hi Quentin,

 

Ive been reading this thread with interest. Sounds like your having fun.

Peters posts are very useful and most useful. An education in all things air flow and fuelling!

 

Anyway..without sticking my nose in, not treading on any toes and before you get too carried away, is it worth going back to basics?

By that I mean out of the factory gates, admittedly the engines were no Veyron, but they didnt hesitate to my knowledge (bit before my time). My tired 69 engine doesnt hesitate, at worst a pop every now and again when I try to give it the beans before its warmed up.

Your vacuum reading does appear to be low (my CP is about 11-ish" at idle from memory). Given that pretty much the only feedback the MU gets from the engine is vacuum (apart from rpm as its mechanically linked to the distributor) maybe its worth revisiting your vacuum, cam, and give Neil a call and he can assist as well if you give him some data to go on. Perhaps beg borrow or steal a CO meter (if not they are cheapish (60 quid on eBay) and a very useful tool to have) and see that your MU is giving you approx 4% CO at idle (as recommended for my CP engine by Neil). He'll get you to check your fuel pressure again...but maybe worth checking again as well as the PRV can stick or a bit of crud can cause it to jam.

Worth asking but does it only hesitate at certain RPM's? Given the MU follows a fuelling track, it could be set wrong (for your cam) or if your vacuum system is leaking (the brake servo, fitting and NRV is a favorite) then for a given vacuum at a given RPM, you could be fuelling incorrectly (lean by the sounds of it).

Given your engine is a little different from a standard CR (you mention is has a saloon lump in it), then its possible you have a slightly different combination of cam, MU, pistons etc that means it needs a proper setting up on a rolling road perhaps? They could then beyond all doubt tell you why its hesitating, and ensure its fuelling correctly all though the rev and power range. Perhaps worth the outlay if it means you get a perfect running engine at the end of it? Just make sure you take it somewhere that knows about the MU. Either that or take it for one run as a base line reading then show to Neil and get him to instruct you what to do from there.

 

Hope this helps, and more than anything hope you sort the issue out.

Edited July 8, 2011 by AndrewP

[Quentin]

This has all taken so much time and effort I've forgotten when the hesitation started I also forgot what I wrote on the opening statement...... There is an interesting clue where I said that I didn't get the hesitation when I revved the engine from the fast idle which obviously points me right back to where I started - worn spindles (TB no. 1 particularly). Sounds daft but I haven't tried that recently though I've tweaked and twiddled the TBs so much since then lord knows whether it will make a difference. I am committed to reconditioning them now (getting CP ones) so will stop effing about until I get them in and tested! I still aim to find out what Cam I have and talk to Neil who has offered to reset the MU accordingly. I am in no doubt, however, that the rolling road is the real answer.. and probably Revingtons down the road. Get it set up for what I actually have - worn and old as it is. Bit pricey though so can't see that happening this year. Just a point on the vacuum though. Shouldn't I be running rich rather than lean if vacuum is lower than the MU is set up for???

I will report back when the new TBs are installed.

Cheers

[Peter Cobbold]

Quentin,

Youre going to replace the present manifolds so you can happily experiment with the present ones, and we can all learn how to kill that hesitation. Try this:

I'm convinced its a lean spike. That lean mix causes the hesitation because the flame is too slow - its chasing not pushing the pistons on the power stroke. You gave the clue: when you set up a fast tickover the hesitation goes - because the c/f advance is helping offset the lean spike. To correct the slow burning we need to briefly advance the timing to give the mixture more time to combust fully. That's easy and very cheap! - using the vac advance capsule. Drill a approx 2mm bore on the top centre-line of no 4 throttle body so that it enters the TB bore about 2mm behind the upper edge of the butterfly when it is closed. (NB the drilling is on the plenum side of the butterfly not the injector side.) In that "throttle edge" position the hole will experience a very high venturi suction as the butterfly opens, but not at tickover and not when throttle is wider open - it experiences the transient suction we need to operate the advance capsule transiently. Glue the pipe to the capsule into the hole. The 'flame trap' is not needed ( thers no petrol in the air!) and is best left out as it adds dead space and will slow the advance mechanism.

Let us know if it works, and in the best interests of everyone even if it does not!

Peter

Edited July 7, 2011 by Peter Cobbold

[Guest ntc]

You are getting to much air before the bang,the cam is telling you that but I know nowt