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May 24, 2020, 11:27:06 PM

acceleration hesitation

This is a discussion for the topic acceleration hesitation on the board Beach Buggy Engine and Exhaust Help.

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this user is offline JohnnyV

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on: September 01, 2019, 09:54:36 PM
Have a query regarding hesitation on acceleration I am getting.
I have an AD 1600 twin port engine in the buggy that came with the car so do not no any history if anything has been done. Since owning the car replaced the manual fuel pump and rod to get it started. After doing the rebuild of the body could not get the engine to run smoothly so replaced the solex 34 pict 3 with an aftermarket carb to get the car running along with a replacement centrifugal distributor.
Car starts and ticks over nicely and revs without problem. When driving from cold car drives and pulls fine but within minutes, as it warms up I assume, develops hesitation when accelerating. Can drop the clutch and increase revs and can power through and car picks up again but suffers every time the revs drop. Apart from the carb issue the engine runs clean and starts without issue.
Have check and adjusted  everything I can. Timing, valves ok, new carb so should be no leaks and readjusted and checked.
Done some reading and some opinions say better to have vacuum distributor ?
Also I have to check for air leaks -carb should be ok but says to check manifold so will do that next.
Carb did come with some bigger jets so maybe worth changing to see if this helps.
If there are any other things I should check any suggestions are welcome.    Thanks


this user is offline pepsi81

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Reply #1 on: September 01, 2019, 10:28:30 PM

Hi,
Not sure. Think you have an auto choke, really need to recheck your post. Sounds like you are running weakish, which can be damaging. Try changing the jets up, then re- checks , then repost.  Presume timing etc is good.Iím sure a grown up will be along soon.
Best Paul


this user is offline pepsi81

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Reply #2 on: September 01, 2019, 10:30:56 PM

By the way. Which type of distributor do you have, 009, SVDA etc. This will affect whatís going on  8)


this user is offline Dave DND

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Reply #3 on: September 01, 2019, 10:36:24 PM
Carb manifold icing ?

Are your heater risers blocked maybe ?    :-\
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this user is offline farmer rob

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Reply #4 on: September 01, 2019, 10:38:04 PM
The 34 PICT 3 carb is designed to work with a SVDA dizzy. If you have a centrifugal only advance dizzy, you will get the hesitation. It might not show up on the cold engine as the choke will still be on for a while. They call it the 009 flat spot, which is most annoying. You can mask it a bit by setting timing to 32 degrees max advance BTDC at 3,000 rev's and by setting the accelerator pump to max squirt. But I would get a SVDA dizzy for it personally. Some times the aftermarket carb's might be set a bit lean which also will not help!

Rob


this user is offline pepsi81

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Reply #5 on: September 01, 2019, 10:46:04 PM

Like Rob says,check your distributor. Better rich than lean.
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this user is offline JohnnyV

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Reply #6 on: September 05, 2019, 08:34:17 PM
Carb manifold icing ?

Are your heater risers blocked maybe ?    :-\


Not much time to work on the buggy this week and away all this weekend  :(
Did a few checks tonight and ran the engine until everything nice and not ..... except the heater risers, only a bit of metal to metal heat transfer. Will need to strip down and investigate. Good call Dave  ;-)up
Also took the air filter off and put my hand over the air intake. Engine stopped immediately and a nice suction ring left on my palm so at least no major air leakage.
I think engine still must be running lean so will probably do some step by step test and change main jet and after richen up the acceleration mixture.


this user is offline pepsi81

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Reply #7 on: September 05, 2019, 08:41:40 PM

 >:( keep us informed. Past me. Farmer Rob or Snoopy are your best bet ;-)up


this user is offline Dave DND

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Reply #8 on: September 05, 2019, 10:11:44 PM
everything nice and not ..... except the heater risers, only a bit of metal to metal heat transfer. Will need to strip down and investigate.

Avoid the rookie error here too - the washers with holes in are supposed to have different size hole to allow the air to flow properly

It doesn`t "look" right, but avoid the temptation to make both holes the same size as it won`t work  ;)
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this user is offline Peter

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Reply #9 on: September 06, 2019, 05:56:30 PM
Hello,

I would without hesitation suggest you do two things before you
do anything else...

First get those heat risers working properly, having a smaller diameter hole in
one of the riser gaskets helps the exhaust pulse to stay inside and warm the manifold, thus transferring heat and not get
pushed straight through, the intermittent firing of the cylinders each side will give the exhaust gasses a 'pulse that
rocks back and forth. This isn't a major issue but its best to have one side with an easier flow path.

The other thing that many, many, people never do is ensure you have HOT air going directly into the air filter airbox,
if you dont have one, ie an air box, then make one, it needs to contain all the heat thats going in there.
Having HOT air is one of the most important things you can do and the carb/sytem will benefit enormously.
This isnt just a suggestion, it a MUST HAVE situation on any single carb setup.

When single carbs are working the air pressure drop below the main butterfly is colossal, ice will form without hesitation
and very fast on the manifold walls and in winter will choke the entire manifold completely.

Ensuring heat is present will mean your carb can be jetted easily and the engine will perform normally in any temperature,
Summer or Winter.

We live in a colder climate than some and VW took measures to solve this issue when designing their air cleaner boxes,
most just chuck them away completely ignoring the fact that VW knew what they were doing, and then complaining after the event
and not bothering to try and 'learn'...

I run a single carb and due to my efficient heat risers and HOT air supplied direct to the air intake/box, she starts, runs, and ticks over
perfectly all the way down to -14 degrees in winter with no issues whatsoever  ;-)up

You MUST do these two things before anything else as it will ensure your carb has the environment it
desperately needs to function.


I get hot air from a sealed cavity thats slipped along my exhaust, it gathers the heat direct from the exhaust tube and lets it waft its way upwards
straight into my air cleaner, the air thats required for the engine to breathe is gathered elsewhere and also enters my air box, whereupon
it mixes with the heat.

Peter

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« Last Edit: September 06, 2019, 06:00:06 PM by Peter »
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this user is offline JohnnyV

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Reply #10 on: September 09, 2019, 10:19:10 PM
Thanks Peter thats some great advice.

Well step one and I have removed the exhaust and found that the short pipes and plates that are attached to them have 2 different sizes holes as suggested. The left hand about 5mms and the right hand side 10mm(according to the drill bit sizes I can fit into them) but importantly do not go through into the exhaust itself so can not transfer any gases in this pipework. I checked the heat risers and although the initial pipes either side are clear I think the short length in the main casting is blocked as I am unable to get anything through and even the airline will not push any air through.
Looks like I will need to strip things down as try and clean out the risers.


this user is offline snoopy

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Reply #11 on: September 10, 2019, 07:54:03 AM
Managed to do the last one with a bit of fencing wire flattened like a chisel on the end and bent to a handle so I could rotate it on the other. Took a while but the airline shifted the loose bits a crap cut after.


this user is offline Dave DND

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Reply #12 on: September 10, 2019, 08:18:28 AM
The left hand about 5mms and the right hand side 10mm(according to the drill bit sizes I can fit into them) but importantly do not go through into the exhaust itself so can not transfer any gases in this pipework.

Thats exactly how I stumbled over this fault - as I had severe carb icing, all of my risers were really clear, which is always the first thing to check, but the exhaust holes in my dual cannons had not actually been drilled through to allow the system to work. I wrongly assumed that because it was all fitted together that the holes would have been there but weren't.  A quick play with a drill and all was well afterwards.

Keep us posted how you get on   ;-)up
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this user is offline Peter

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Reply #13 on: September 10, 2019, 09:43:41 AM
Yes, as Dave has said, do say how you get on.

I took things a little bit further as I was in a position to be able to make a few things,
I do realise that not everyone can do this though.

After going through several sets of heat risers on my single Weber manifold, which, due to their construction and materials,
just rust away flaking apart and failing pretty quickly, specially when used daily for many years.
I made up stainless steel receivers and used standard central heating copper tubing, the end result
has been fitted for many years and is still in the same state it was when fitted.
The copper tube to receivers fit is very close and it has meant I dont need any sealing goo, as
the copper tube just heats up and swells in its seating, sealing in the process. I attach a picture below,
its a bit grubby I'm afraid, mainly due to being used  ;-)up

Quite a few issues with carburation can be overcome by just looking at whats happening and
making the effort to understand and sort things out.
Far too many just faff with one or other thing never achieving the goal and then just letting it go proclaiming
its all faulty, which is a great shame as the engines we all use need certain things to be taken care of from the outset.

This icing issue is something that affects all engines so its worth the effort to eliminate, sometimes
things dont 'look' as nice as we would like but the trade off is that you can drive smoothly in very cold conditions.

Twin carb setups will still be icing, but due to the short and much warmer manifolds the ice wont 'stick' and build on the manifold walls,
hence this issue is not so noticeable, its still happening though.

Having a HOT air supply with twin carbs too will make a big difference to the jetting and general running of the engine,
I run my hot air supply all year even in summer.

Peter

« Last Edit: September 10, 2019, 09:46:26 AM by Peter »
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this user is offline Merscury

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Reply #14 on: September 10, 2019, 12:34:01 PM
I've got to agree with everything Peter says on this subject he really knows about this, I also have a central weber and without both good heat risers AND a hot air intake it will ice. Like Peter I ditched the weber heat risers and made my own but did the opposite to Peter in as much as I used a 3/8 bsp x 15mm copper plumbing fitting in the central manifold and made stainless steel risers. Initially I took hot air from the surface of the cylinder head but in winter the cold cooling air means it take too long to heat up enough so am half way through making a stainless heat exchanger/collector that will fit over the exhaust where it exits the cylinder head. Just got to weld it up and cut out the sides so it fits over the exhaust pipe. (you can see the scribed marks on the side where I need to cut out)

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