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Kirkham Motorsports

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  • 1 Post By blykins
  • 1 Post By A98Coupe
  • 1 Post By Gaz64

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Old 05-06-2017, 05:06 AM
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Default Beware of poor quality castings on Quickfuel carbs

Dear All,

I thought it about time to share my frustration & problems with a pair of custom built Quick Fuel carburetors which were provided by my engine builder on my new Shelby 468 FE with 2x4 medium rise set up.

When I first got this motor running, it suffered from bad surging at light load cruise and also ran on after ignition off. I got big improvements by changing to an MSD programmable ignition unit and was able to run with much more advance at lower rpm/ higher manifold vacuum. I also installed an Innovate LM2 O2 sensor & data logger so that I could record AFR, MAP & RPM so that I could get the carbs dialled in.

However, I could never get a stable AFR at cruise. Sometimes it would run OK in the high 13s / low 14s, but then it would suddenly go rich into the low 11s and the rear of the car would be covered in black soot. I stripped the carbs several times, checking pwr valve function and replacing gaskets and this is the list of issues I found. Maybe this is useful information for you?

1. Power valve blow-out protector ball on front carb was sealing against throttle plate so vacuum signal was not getting to pwr valve and this was the cause of the engine running rich intermittently at cruise & light acceleration. I solved this by drilling a 1mm hole into the check ball chamber in the throttle plate to allow air the pass freely out of the pwr valve chamber.

2. When checking metering block gaskets to ensure all ports were aligned properly, I found that the timed spark port gallery (which is not used on these carbs), was completely open from the side of the metering block (which isn’t tapped for a fitting), through the metering block and into the main block exiting above the primary throttle plates. This allowed unfiltered air to pass into the engine when the primary throttle plates were open, not a big issue, but poor attention to detail from Quick Fuel! I filled the main block drilling with metal epoxy so no problem now.

3. Front carb primary fuel bowl had a hole into one of the accel diaphragm screw tapping which allowed fuel to leak out. I had to repair that with metal epoxy. Again, poor quality from Quick Fuel.

4. Fuel always seemed to drain down quickly in the fuel bowls after stopping the engine, some throttle plate always appeared wet and fuel would leak out through the throttle shaft onto the inlet manifold as well as into the engine! The manifold floor was always wet and No.8 cylinder always had fuel sitting in it! I stumbled across the root cause after removing the primary metering block to increase the size of the IFRs so I could start to tune out the surging. However, both power valve chambers had fuel in them - again. I checked the power valves again with a MityVac and they were both good – no rupture – so where was the fuel coming from? I found the problem whilst blowing out the main block with compressed air. I found that the main block drilling which connects the power valve chamber to the throttle plate, is also connected to the accelerator pump gallery! I’ve attached at YouTube link below to show you what happened when I pressurised the accelerator pump gallery with air after filling the pwr valve chamber with WD40. Bubbles escape! This is how fuel is getting into the power valve chamber and of course into the engine when it shouldn’t. This will also reduce the vacuum in the power valve chamber and cause it to open sooner than it should, or even stop the valve from completely closing.

It would appear that the Quickfuel/Proform blocks on both carbs have bad porosity from poor casting process are they are both now junk.

Over the past 6 months I've tried to find some replacement carb main bodies through my engine builder but I've now given up chasing him and so I'm asking if anyone out there knows who I can contact to get some replacement good quality main bodies so that I can re-build these carbs. For reference, both carbs are model 4160, 600CFM vac seconday, downleg boosters, adjustable air bleeds & IFRs.

Thank you

https://youtu.be/SvssRUCEgZI
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Old 05-07-2017, 04:45 AM
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This really stinks. I was planning on going with a 750 from Quick fuel because I have heard nothing but great things about their carbs. My local carb specialist also said they were the best. I was tossing up a new Holley HP or the quick-fuel 750. I am going to print your post and call him to discuss.
Thank for this valuable information...Dave
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Old 05-07-2017, 09:52 AM
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Dave,

These carbs were purchased by my engine builder back in 2013, so Quickfuel may have got their act together and sorted the problem out by now. Back then I suspect they were getting their castings in high volume and very cheaply from China - hence **** quality!

Anyway, I just wanted to raise awareness just in case anyone has or is experiencing similar carb issues.
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Old 05-07-2017, 12:00 PM
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99% of the carbs I use and sell are Quick Fuels.

I would be very slow to lump *all* QFT carbs in the same bunch and I would suggest not to do that.

Every manufacturer that builds more than 1 of anything will have a statistical number of products that have issues. It's just part of the game. I have heard people gripe about Quick Fuel, Holley, AED, Pro Systems, and Braswell. You will never have a company that will make 100% perfect products.

I would recommend RAM and McLeod clutches over all others. However, I have sent a few of each back to the manufacturers over the years for issues.

A98, I would be more than happy to try and get parts for you if you want them. Holley bought QFT several months back and things are more difficult there for customers, but I have an "in".....

David, please don't let this post sway you in your purchase. In my mind, QFT carbs are among the very best out there.
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Old 05-07-2017, 01:15 PM
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I have a quick fuel and love it. Mostly because of it's adjustability. That being said I had problems when I first bought it and after a lot of initial frustration I found when they built it someone forgot to put the spring in the power valve protector. Quick Fuel sent me fix kit and new gaskets. Quick Fuel uses all Holley parts and is owned by Holley.
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Old 05-07-2017, 02:04 PM
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Default Porosity Explained

Like Blykins stated, manufacturing defects will occur and hopefully they will be addressed with great customer service. If ‘porosity’ is the root cause of your problem or ‘leak’ issue I can shed some light on the topic since it is not understood by the average consumer:

For many years, I have been working in the OEM die cast component and tooling (molds) that produce complex parts. All our die cast/machined components must meet NADCA “pressure tight” requirements so they don’t produce fuel or vacuum leaks (both internal and external).

With this said, all die castings will have some level of porosity/voids. Both die cast and plastic injection tool designs are fine tuned with mold flow analysis software that points to potential trouble areas. Part wall thickness, radii, gating, venting, cooling, and many other factors can reduce or move the porosity to less critical areas of the part. Also, when any machining is performed on the die cast part, the cast “skin” is removed and this opens up porosity that lies under the surface.

At the end of the day, a percentage of die cast parts will leak fuel or air. For critical parts, typically, a pressure decay test (100% of the parts in our case) is performed on the machined part to determine the leak rate. If it falls below a determined maximum leak rate, the parts can used as is. If the leak rate is too high but below a maximum rate (too large of voids) the part is impregnated. The impregnation process uses a ‘sealer’ through a thermal or vacuum method that will fill the porosity voids in the die casting. Now you have a ‘pressure tight’ die cast part.

Hopefully, your parts can be returned and the manufacturer should take the leak seriously. Nobone wants a potential fire from a gasoline leak that could be traced to a manufacturing defect.
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Old 05-08-2017, 06:38 AM
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Blykins,

I hear what you say about a certain % of products are expected to have some kind of defect, but I have a 2x 600CFM carbs and both exhibit the same porosity problem which I showed in the video link. This can only come about through a bad batch of castings and depending on QFT's manufacturing batch size at that time, quite a lot of people could be experiencing similar issues to me. This is why I thought I should bring it to everyone's attention. A carb which doesn't control fuel properly could cause engine damage or cause a fire - as Jeff pointed out.

Anyway, thank you very much for your offer to contact QFT for replacement parts. That is very kind of you. However, my engine builder also had a QFT contact but after 6 months of trying, eventually led to nothing. So yesterday I ordered 2 completely new carbs in the hope that the quality of the castings has improved. I wish I'd waited a little longer to see more replies to this thread......I would have taken you up on your offer before spending a further $950 on carbs from Summit Racing. Yes a bad experience for me.
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Old 05-08-2017, 11:08 AM
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We use QFT exclusively as well and never had these issues. As with any products there will always be an issue or two. We have used hundreds at this point and I would highly recommend a QFT carb. If anything you might stick with their billet metering blocks and base plates to avoid this issue. Hate to hear anyone has had issues.

Thanks
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Old 05-08-2017, 03:32 PM
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I don't see any mention of fuel levels versus hot shut down percolation.

Can you post a pic of the power valve blow out protection as you have described in Point 1?

And was this only one carb?

How much fuel was in the power valve vacuum cavities?
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Old 05-09-2017, 04:54 AM
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Quote:
Originally Posted by Gaz64 View Post
I don't see any mention of fuel levels versus hot shut down percolation.

Can you post a pic of the power valve blow out protection as you have described in Point 1?

And was this only one carb?

How much fuel was in the power valve vacuum cavities?
Gaz64,
Answers to your questions:

1) Fuel levels were set mid sight glass as per QFT instructions. I did get some hot shut down fuel percolation when I first got the motor running, but sorted that out with phenolic carb spacers. However, that was not the issue. Fuel would simply leak outside & inside the engine after priming the carbs with the electric fuel pump and not even starting the engine! Both carbs had the same issue.

2) About the blow-out protector, I'll try to post some pictures if I can work out how to reduce the file size, but I probably should have mentioned that neither carb had the return spring below the steel ball (like Holleys), so the ball simply drops into the brass seat which just happened to be a nice seal and stopped the vac signal reaching the pwr valve chamber. Rather than punch the ball & seat assembly out & install the correct ball & spring, I simply drilled a hole into the seat to allow air to pass freely. Anyway, poor workmanship from QFT.

3) Everytime I removed the metering block, the pwr valve chamber had fuel in it and the rubber diaphragm was wet. I always checked the pwr valves with my Mityvac and they were always good - i.e. no rupture. Fuel should not get into the chamber unless there is a leak path through the casting.
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Old 05-11-2017, 10:42 PM
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Some good points there.

I generally run window carbs in the 1/3 - 3/8 up, just under half.

Now I need to do some more research,

Last edited by Gaz64; 07-17-2017 at 10:53 PM..
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Old 05-12-2017, 04:42 PM
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It sounds like you have two carbs assembled by the same tech who left the power valve protection ball springs out on assembly?

I can't see anywhere that QFT does not use the spring like Holley does.

Clearly the spring keeps the ball open in both directions for normal valve operation.

QFTs instructions:

1. Remove throttle body from main body
2. Locate the power valve vacuum passage (note: small hole next to the center
throttle body screws pri. & sec.)
3. Check the drill collar height this should be 9/32” of the drill point exposed)
4. On the main body surface of the throttle body, drill the P.V. vacuum passage until
the drill collar contacts the gasket surface.
5. Remove all chips and deburr if necessary
6. Install the spring provided with the large end of the spring at the bottom.
7. Install the check ball.
8. Position the new seat in the hole and lightly tap it with a drift and small punch until it
is flush with the gasket surface.
9. Reinstall the throttle body.
P/N 99-18
© Quick Fuel Technology 2012
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Old 05-14-2017, 02:52 PM
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Thanks Gaz64.

Yes, I agree these carbs were put together by someone who either didn't know what he was doing or simply didn't care. Point No. 8 was another thing QFT got wrong. The brass seat wasn't punched flush with the gasket surface & was sticking up, which prevented the main body sealing properly with the throttle body. Simply poor quality & bad workmanship all round. Shame I paid $1,200 for the privilege!

On the plus side, the whole experience has made me much more knowledgeable about re-building & tuning these carbs.
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Old 05-15-2017, 01:37 AM
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As a data point, I have a brand new QuickFuel 750-AN which was installed by my engine builder one month ago 4/2017. This carb has performed well and show no leaking or poor castings what so ever. OP, I think perhaps you had a questionable custom build on your carbs?
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