More weber questions

[bigdog]

I'm so darn frustrated. I've always been good at working on cars/bikes and have built hotrod Chevy LS engines.But this little English crossflow/weber set up has me nearly to the point of calling a guy named Guido & having the car become missing.

As some of you have seen in my posts. I have had quite a few issues with my 1600 crossflow. I ended up with new valves sitting in new hard seats. A new set of piston rings and bottom end bearings. Ignition checked out fine.

But I was still suffering poor running particularly at just off idle. A fair bit of spitting even when warm. I did a check for air leaks and found one on the front carb throttle shaft.

As it's hard to have webers worked on in my rural part of America. I just said to heck with it and bought two new ones, Along with new o-rings & grommets for the isolators.

I must say that the car does run much better. Yet at times it has me totally confused.

Take the slow circuit. Most guides say that a 1600 sprint (110HP)  engine should run a 45F9. When I did this, The spitting out the intakes was such that I nearly set the K&N filters on fire. (they were smoking) so in goes a set of 50F9's, Much better. But here is were it has me scratching my head. Upon cold start & first setting off, It is a bit finicky and spits a bit. (expected) As it warms up it runs great. However, after the engine is at it's hottest (stop & go traffic) It will start to spit again just off idle like it's gone lean. That shouldn't be. It should be richer as it warms up. The engine idles smooth at 800-900 RPM

My jetting is as follows:

40DCOE

30mm choke

35 pump jets

4.5 aux venturi

50F9 slow jets, 1.5 - 1.75 turns out on idle screws

120 main jets

170 air jets

F16 E-tubes I do have a set of F11's from the new carbs.

 

 

[zetec]

I had so much trouble with carbs over the years I ditched the whole lot & went TB & injection.

now when I drive it I get no issues- bloody fantastic.

when (Mr Weber) tells you it takes 95% to getting close but takes a lot longer to get it right- I threw the towel in.

i shall have a look into my old set up & let you know.

have you tried adjusting (on idle) the mixture screws till the engine note is at it's highest?

this seemed to get it about right for me

[zetec]

Ignore the 'new carb ' jets- they put standard jets in new carbs which are useless to most applications- stay with what you got & start from there- 

also look up mk1 & mk2 xflow carb jet settings this might help.

[zetec]

Get the carbs balanced really well. Without this, you will be losing from

the start.

[bigdog]

 

Thanks for your input zetec

As I bought new carbs, I still have the old ones & I did transfer over the old main, slow, Air jets. As well as the e-tubes. But as the car hasn't been right from the start. I.E. Burnt valves & a failed leather style throttle shaft seal. (vacuum leak) It's been hard to get a base from which to start. And I seem to have run into the issue that I have heard of with webers. In that in some cases, Rich acts lean or lean acts rich. Or some such thing.

The one remaining test (taken from the weber book) is to kick up the idle an additional 400 revs with the idle speed screw. Then adjust the slow speed flow screw (mixture) to see what that does. Allegedly, this will tell me if it really is rich or lean despite the smooth idle and 1.5-1.75 turns out on the mixture screw.

The carbs are balanced to within a half needles width or so on my synchrometer.

I have never had so many issues with a set (actually two sets) of carbs. I had very few carb troubles on my 356 speedster that ran a very hotted up 2.3 liter type 1 bug engine. 170HP 171 torques running IDF's meant that it was a very stressed air cooled engine which started life as a 36HP lump and had a very complex rube goldberg throttle linkage to run those IDF's. The xflow should be a dawdle. But it isn't.

I'll have a go at googling the Mk1 & 2 base line settings.

I'd love to switch from carbs to F.I. But I'm afraid the wife will have none of that. I sold a very nice Zed 4 3.0 SI (that the wife & I loved) to fund the 7. So she see's the 7 as a rather big step down from the Zed & with the issues so far, She has a point. We were very happy with the Zed, But I wanted something unique. I just hadn't counted on uniquely troublesome.

[Paul Deslandes]

you could try PM 'ing Roger King if he doesn't pop up soon.  I think he responded to one of your earlier threads so you should be able to find him.

[bigdog]

I'm sure Mr. King will see my post in due time. I just need to be patient.

[Roger King]

I only have a few comments.

On 30mm chokes, I'd be inclined to come down a little on the mains - 115 perhaps. You are advised to have it rolling roaded though because all installations are different.

Secondly, spitting on light throttle with 45F9's is really common. Generally 50F9 is better as you have discovered.

I can't explain why it gets worse when very hot, but I would suggest checking to make sure the underbonnet temps aren't allowing the fuel to vapourise and also check float levels. If you have the black floats they should be at 13mm. Check fuel delivery is adequate too. You could try setting the idle mixture screws a tiny bit richer than at present to see if that helps.

 

[bigdog]

Thank you Mr. King.

I run the 7 sans bonnet on the next hot day & see if that makes a difference.

 

[Jim_Harvey]

I have also spent a lot of time trying to cure the cold flat spot and spitting back throught the carbs.

My car is a 1700 crossflow with twin 40s, 234 cam, ported head with 41.3/34.9 (1.625"/1.375") valves.

Current jetting is: (original jetting in brackets)

Main venturi 36 (32)

Main jet 130 (120)

Air corrector 180 (165)

Emulsion tube F16 (F16)

Idle jet 50F9 (45F9)

I also found changing to a 50F9 idle jet cured the spitting.

Changing the main jet and air corrector made the car more tractable and largely cured popping and banging on the overun.

Setting the float levels very carefully reduced the flat spot but has not completely eliminated it. I set the float level (with the carb cover held vertically) to 10mm Min and 15mm max. This gives a fuel level of 32mm from the top of the body to the fuel surface measured on the shallow (engine) side of the float chamber.

Boring out the venturies from 32 to 33,34 then 36mm has made very little difference. At 32mm it pulls like a diesel,lots of grunt but no top end, at 36mm slightly less grunt, slightly better top end.

I have the old style O-ring seals between the carbs and the manifold, with seperate o-rings each side of an aluminium carrier. I have changed the o-rings to Viton ones. I spent a couple of hours setting the gap between the head and manifold as equal as possible using feeler gauge stack to ensure the o-rings were clamped uniformly.

Finally, I was not impressed with the Aldon distributor fitted. When I removed the springs from the counter weights, the movement was very sticky. The pivot holes were not a very good fit and weren't very square to the face either. I drilled them oversize and made some brass bushes which were pressed in place. One weight acts against the other and has a cam profile. The surface of this was very rough, so I have polished this to achieve a smooth action. I like to think it now works properly.

The springs weren't right either. They started to advance at about 1800rpm and were still advancing at 4000rpm.

My car runs a lot better now than when I first got it. Its always been a bit temperamental when it gets very hot and is prone to stalling at tickover.

I hope that this might be of some help to you.

Jim

 

 

 

 

[bigdog]

Thanks for all the information Jim.

Since my last post I did do a detailed look at the synchro flow numbers for each individual carb barrel and found that each carb had one barrel at 3 and the other was 2.5. I looked at the throttle plate position through the progression hole inspection cover and all were covering half of the first hole. So I adjusted the air bypass screw to balance them. That seemed to help a bit as all the carbs are now matched.

I did as Mr. King suggested and dropped the main to a 115 and adjusted the floats to 13mm with a 6-7mm drop. As per the ignition, All I was told by my mechanic was that it was electronic & not points. He was replacing the valves so didn't do anything with the dizzy.

I do not get a lot of popping on overrun from higher revs when I totally close the throttle. The popping (both from the carb and the exhaust) are at slower speeds around town at partial throttle. It gets worse when the engine is hot.

Overall the car is much improved from when I first bought the it.  Last week I logged 22MPG US or 26.5MPG imperial, which is nearly double from what I was getting prior to  the valve job and new carbs. So things are looking up, But that last bit of tuning is proving elusive without the rolling road. Unfortunately I have yet to find a rolling road in my area that isn't booked up for the summer.

I'm hoping to buy a trailer from Mr. David Saville Peck in BC (Caterham Canada@ super7cars.com) So I'll be able to travel to get some dyno tuning time. In the mean time, I can live with how the car is running.

[Molecular--Bob]

Get yourself on the back up short notice list with your local rolling roads, people often have last minute problems that prevent them turning up. An alternative might be to get yourself a cheap wideband set up, then you could at least see where it is going lean or rich. Then you can work on changing the right parts.

[zetec]

Stick with a local busy rolling road!     Make sure they can sort carbs- many can't - I've spent good money & not been happy.

as above wait for a cancelled booking - if they are busy they are good!!!

Dont look at other cars with carbs because they are heavier & go 'on throttle' a lot more than our little light cars. So their settings won't help.

a rolling road will help iron out flat spots & sort out mixture etc- she"ll be fine afterwards

 

 

[bigdog]

I was seriously considering a wideband sensor. here I even had a sensor bung welded to the pipe just after the collector, Then the silencer internals went wonky and no more bung. At least now I can hear my self think and the ringing has subsided.