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Learning how to build Lotus Seven replicas...together!
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PostPosted: May 30, 2018, 9:07 am 
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Looking fabulous!

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: March 25, 2019, 12:58 pm 
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Joined: December 29, 2007, 10:41 pm
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Location: Vancouver, BC
I guess I should bring this thread up to date... last October I managed to get the car through the "out of province inspection" which then allowed me to license the car for the road. Originally the car was sold in Ontario, but sometime after 1984 it came out west in pieces so was never registered here in BC. Obtaining the title was relatively easy, but did require some back and forth with ICBC (the insurance provider/DMV/dumpster fire). I did get a few days of driving in before the winter took hold, and all I can say is wow it's fast!

In December I ordered some one piece side windows from the UK, as trying to make they myself turned out to be a bit more difficult than expected. They have a compound curve, which I couldn't replicate. Anyways, they arrived and I spent the better part of January fitting them (weekends only):

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Next up was this months purchase, a new cam cover. The engine bay went from this:

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To this:

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Unfortunately, it added weight, but it looks better in my mind. Other than that, I re-plumbed the fuel system two weekends ago as the motorcycle fuel pump didn't like where I had mounted it. So it was repositioned to just in front of one of tanks, meaning it's always primed (or flooded). This has made it less noisy and seems to keep pressure with less effort.

This past weekend I renewed the insurance and started back to the road testing. I played around with the carbs and timing but I can't seem to cure an off idle stumble. I'm running carbs off a CBR900RR so it will take some time to figure out. I have some theories that will get tested the next time I'm in the shop. I also noticed a weep of coolant from the thermostat housing which appears to be coming from where they're glued together, so a new one is on its way.

Anyways, it's sure fun to be driving it again and hopefully in a few weeks it will be reliable.

Rod


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PostPosted: March 25, 2019, 6:38 pm 
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Location: BC, Canada. eh?
Weber 45DCOE's are famous for off-idle stumble on Zetecs, to the extent where they actually make one-off, brand new, model specific ones for the 2.0 "blacktop" Zetec.

I'm not an expert, but my understanding is that the Zetec breathes SO well, on the slightest RPM increase, that carbs have a hard time keeping up with fuel, causing the engine to run extremely lean for a moment & stumbling. The new version of 45DCOE's have extra progression holes to feed extra fuel during this critical progression.

Is it possible that a brief & sudden lean condition, owing to a situation similar to the above, is causing your issue?

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PostPosted: March 25, 2019, 7:07 pm 
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Location: Vancouver, BC
zetec7,
So far that's my thoughts, a lean condition. I didn't have a good look at the carbs before bolting them back on, but I had hoped there was at least a progression hole that the butterfly uncovered when going off idle. Unfortunately, that's not the case. Had there been a progression hole, I would have tried some larger idle jets. So, the next step is looking at blocking off the air jet (or passage) for the main jet emulsion tube. Some guys in the UK recommend it for the Fireblade (or CBR900 in my case) carbs. It should be an easy test the next time I'm in the shop, just a bit of tape over the holes then try it out.


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PostPosted: March 25, 2019, 8:05 pm 
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Location: BC, Canada. eh?
Good stuff! :cheers:

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http://zetec7.webs.com/


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PostPosted: March 26, 2019, 8:01 am 
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Location: 4AGE in S.E. Michigan
" just a bit of tape over the holes then try it out." DO NOT BLOCK OFF THE PORT HOLE TO THE EMULSION TUBE. Try just a piece of thin metal roll into a tube shape that you can slide over the emulsion tube. [more gas friendly] You only need a thin section, only the top two or three holes depending on the hole size and spacing. [some carbs have very small holes] you can also try a "C" section tube that allows some emulsion tube holes to be uncovered, while other holes blocked off.
Also look for kits that allow you to raise fixed needles on the newer style carbs.
You can also try getting slides with a smaller cut-away or machine a little off the bottoms of the slides.
The last option is restricting the air channel to the top side of the diaphragm, which can be tricky without fitting jets. Do not play with the springs, you will not get them all equal. You could possibly try spacers under the springs.
Davew


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PostPosted: March 26, 2019, 10:05 am 
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Location: Vancouver, BC
dave,
The plan isn't to block the holes on the emulsion tubes, but to restrict the air jet (orifice?) on the face of the carb. It's an easy thing to try as it only requires removing the airfilter and the plastic covers on the front of the carbs. I've read about blocking them from a few sources, so the thought is why not try it. If it works great, if it doesn't then it's back to looking for an alternative solution. Here's a stolen pic of what I'm planning on blocking (or maybe just restrict depending on how things go):

Image

As far as needles go, the carbs already have dynojet needles and are on the middle groove. The main jets are 160's. At WOT it howls, at idle it's smooth, it's just getting off idle that's the issue.


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PostPosted: March 26, 2019, 10:40 am 
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Location: Carlsbad, California, USA
Rod,

Your build keeps looking better and better. It's quite an accomplishment.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: March 26, 2019, 3:15 pm 
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Location: North Van., BC
I ordered some one piece side windows from the UK, as trying to make they myself turned out to be a bit more difficult than expected.

Well that's an unusual occurrence :D

Really like the look and the way they open.

Love that shade of blue.

Glad you got it registered without a last minute foul up.

Ron

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PostPosted: March 27, 2019, 8:19 am 
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Changing the Air Correct Port jet will affect the whole mixture range!
You only want enrichment at the transfer from idle to low needle setting.
You need to raise the needle or reduce the amount of air introduced at low needle settings i.e. blocking the emulsion tube holes at the very top.
The last option, You might be able to find needles with different taper and or smaller shank size, but that does not seem likely with the newer carbs. [in the old days you had 50 needles to choice from]
Davew


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PostPosted: March 28, 2019, 12:23 pm 
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Location: worcester county, Massachsetts
Can't see the pictures...?

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PostPosted: March 28, 2019, 7:38 pm 
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I guess these are keihins. If everything is clean and there are no vac leaks, if the idle mix screw is not happy close to 1-1/2 out, I'd look at a couple numbers larger pilot jet. Should be about $20 for four. Pilot aids at 1/4 throttle or less.

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PostPosted: March 29, 2019, 10:16 am 
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I had the same issue on a Harley with that carb using the Dynojet needle. I tried everything - shims, jets, needle height... always had the same problem you are having off-idle. I went back to a stock needle - poof! Problem solved. Not saying that's your issue, just sharing my experience.

BEAUTIFUL build!

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PostPosted: March 30, 2019, 12:50 am 
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cs3tcr wrote:
I played around with the carbs and timing but I can't seem to cure an off idle stumble.

I'm guessing these carbs lack an accelerator pump used on auto carbs to solve the off idle sag/stumble, correct?

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PostPosted: March 30, 2019, 6:11 am 
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Large displacement applications with a single carb have accel pumps. One carb per cylinder apps don't.

Cs3tcr, a larger pilot jet will shift the best idle rpm adjustment, but the throttle transition is not controlled by the screw. If it did, there would be little point in having a larger pilot.

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