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Wed Dec 17, 2014 1:08 pm

Just looking for a couple of suggestions. I have a rebuilt 1600 dp that I put in a 71 westy and I'm not getting it to idle very well. It seems to cycle high to low rpms and back. When it's cold and still on the cold idle setting, it is fine. But when it kicks down it will eventually shut down because it idles too low.
I'm pretty sure it's a vacuum leak somewhere. It just might be the booster but it was working fine when I had another motor in it. I went through and replace all the booster line just in case and it's still the same. I have the check valve in properly, timing is correct and the carb should be adjusted at least pretty close. I just had the long block rebuilt and am using all the same parts there were on it before and they worked fine then.
Just wondering is there's something I might be missing. I think it's odd that the booster was working fine and now it might be leaking but I think it is the original booster in there.
Any suggestions before I take out the booster for a rebuild? Thanks!!

Wed Dec 17, 2014 1:25 pm

71whitewesty wrote: Any suggestions before I take out the booster for a rebuild? Thanks!!
Cap the nipple on the manifold to confirm. The issue may not be the booster but the hoses leading up to it, especially after being disturbed during the engine drop.
Next try slowly unscrewing the smaller screw on the side of the carb until the idle improves.

Wed Dec 17, 2014 1:43 pm

Thanks Busdaddy, I'll cap off the manifold and see how that works. I also have a vacuum tester that I'll hook up and see if I can get any vacuum to hold on it. I do notice that the booster vacuum doesn't hold once I turn the bus off. It seems to me like it's somewhere along the booster lines or the booster itself but was wondering if there's something else I should also check that I'm not thinking about. I'll report back once I get some time this eve to look at it again.[/i]

Wed Dec 17, 2014 2:20 pm

71whitewesty wrote: I do notice that the booster vacuum doesn't hold once I turn the bus off.[/i]

This is important. After the engine is shut off, you should get at least a few fully-assisted stops out of a boosted system before the pedal becomes hard. SGKent mentioned a good set of test numbers for a good and no-good system that I can't recall, but if it gets hard immediately, the leak is likely in your booster.

You could compare the questionable '71 white Westy with a known good '71 white Westy...

Robbie

Wed Dec 17, 2014 2:21 pm

After you cap your break booster line, spray some carb cleaner around your rubber boots around the carb manifold, your manifolds where they bolt to your heads and the base of the carb.

I had the exact symptoms you're describing. It was my boots leaking.

Wed Dec 17, 2014 2:23 pm

I'm thinking that you have derailed onto the booster as the issue. After you plug that vacuum nipple and take the booster out of the equation, start the engine and spray some kind of brake cleaner around the variuos places where you could have a vacuum leak. Listen for changes in the engine as you spray.

Wed Dec 17, 2014 4:42 pm

as mentioned by others, dual port boots are notorious for cracking and leaking air. What you are experiencing is a common symptom of a cracked boot.

Wed Dec 17, 2014 5:31 pm

Thanks for all this. I haven't looked at it again yet bit I'll be out there in a bit.
The engine has about 500 miles on it and I put new manifold boots on and all new gaskets etc. not to say the they aren't leaking but I know they are not cracked. I'll spray some carb cleaner around.

Asiab, I have two identical busses and I took the motor out of this bus and put into the other one and just put the new rebuilt motor in this one and now the vacuum leak problem started. To compare the two busses, they both stop the same and all brakes work well. I know the feeling of a non working booster and these both work well other than once I turn it off, this bus seems to leak down a lot faster. This is a new symptom since I put the rebuilt long block together.

I'll report back after I take another look at things. Thanks for the suggestions.

Wed Dec 17, 2014 5:45 pm

SGKent wrote: as mentioned by others, dual port boots are notorious for cracking and leaking air. What you are experiencing is a common symptom of a cracked boot.

I see this happen even to new boots when the installer clamps them down then secures the intake manifolds. The manifold side pieces AND center piece must be secured before you put the clamps on the boots.

Robbie

Wed Dec 17, 2014 6:08 pm

71whitewesty wrote:
I put new manifold boots on and all new gaskets etc.

I had a friend install new boots on his dual port engine. He had vacuum leaks like crazy with the same symptoms. What he failed to do was shift the boot and push the boots all the way up and onto the end castings. He wondered why the original clamps maxed out before getting the boots tight.

Wed Dec 17, 2014 6:39 pm

71whitewesty wrote: Thanks for all this. I haven't looked at it again yet bit I'll be out there in a bit.
The engine has about 500 miles on it and I put new manifold boots on and all new gaskets etc. not to say the they aren't leaking but I know they are not cracked. I'll spray some carb cleaner around.

Asiab, I have two identical busses and I took the motor out of this bus and put into the other one and just put the new rebuilt motor in this one and now the vacuum leak problem started. To compare the two busses, they both stop the same and all brakes work well. I know the feeling of a non working booster and these both work well other than once I turn it off, this bus seems to leak down a lot faster. This is a new symptom since I put the rebuilt long block together.

I'll report back after I take another look at things. Thanks for the suggestions.

I would just like to chip in:

there are two kinds of brake cleaner. The chlorinated stuff turns into incredibly poisonous gas (WILL kill you) above a certain temperature. NEVER leak test with brake cleaner.

Carb cleaner is OK but not that sensitive. Some rubber does not care for it.

Starter fluid is very sensitive and will raise RPMs at the slightest leak. Being the most flammable of the bunch (pretty much strait ether) keep a fire extinguisher very handy.

You can also do some leak testing with brushed on vaseline. Bit messy but very safe and will plug a leak for the short term.

You can also find leaks by listening. You don't need the fancy HVAC tool for this. Try a very long necked narrow funnel. Put the narrow end around suspected spots and listen to the wide end. This also substitutes for a mechanics stethoscope for listening to valve noises, etc. Gives a different and less sensitive tone for mechanical noises which can be handy. Good for listening for spark leaks under the tin (the snaps really sound off).

Wed Dec 17, 2014 9:12 pm

So I just went out and disconnected the hose from the one way valve and capped off the manifold side. Runs like a champ now.
I also forgot that I didn't replace the hose from the check valve through the fire wall that goes to the long metal tube under the bus. It's a bit crusty. I think I'll replace that piece first and see if I get lucky. Otherwise I'll have the booster rebuilt. I did that on the other bus already and it's great now.
Just odd timing that it decided to go during an engine swap. It's just a stock 1600.
Thanks for all the suggestions.

Wed Dec 17, 2014 9:27 pm

The hose I use is Gates 27231

http://www.oreillyauto.com/site/c/detail/GAT0/2723...;ppt=C0267

Thu Dec 18, 2014 9:45 am

Thanks Aeromech. I went to the local napa to pick up some of that hose. They didn't have the gates number on hand but had "their" number as a substitute.
So I have 15/32 VL 09/30/90 MO9300. It looks a bit smaller ID but the counter guy says it should work fine.
I'll give it a shot today and report back to see if I get lucky with just a hose replacement.

Thu Dec 18, 2014 12:06 pm

71whitewesty wrote: ... see if I get lucky with just a hose replacement.

People have gotten lucky with less I think. :lol:

Thu Dec 18, 2014 4:26 pm

Well the hose I bought was a bit too small I decided, so I took it back and got another type. I've used this on my other bus for the last 5 years or so with no problems. It's a 19BPlant master multi purpose 1/2 " or 12.7mm 315 psi, got it at. Napa. It's red on the outside and black inside. It's stiff but I'm sure it doesn't have the wire reinforcement.
I just installed it and the problem is fixed.

Busdaddy somehow felt his way through my description and nailed it.

It appears that it was probably leaking where it went through the fire wall. When I was pulling the hose off the metal tube in the front, it just fell apart. It must have taken a jostling somewhere along way when taking the engine in and out and kinked at the fire wall. If you take the hose and bend it in half with your hands it crumbles.
I would suggest if any one has the original vacuum hose still on there that it's time to replace it. It's easy to do.
So I feel lucky because I didn't want to deal with the booster right now. However I believe my main seal is leaking on my new rebuilt engine....
I will re-time and tune things again without the vacuum leak and then pull it out and deal with that main seal. :?
Thanks for all the help and suggestions.

Thu Dec 18, 2014 5:46 pm

Nice. I like when the first solution is the culprit! Do you think it will withstand the 25"/hg of vacuum without the reinforcement? It would be interesting to try to squeeze the hose engine off, then on, then while someone hits the brakes.

Thu Dec 18, 2014 5:51 pm

Cool!, time will tell if it stands up to vacuum with no wire, it'll usually suck closed and cut off the booster on a hot day when you are pulling up to something and suprise you with a less than power assisted stop, be careful.

Did you change the hose at the front between the metal tube and the booster too?, that one can't be in any better shape.

Thu Dec 18, 2014 9:57 pm

red cover black center sounds a little like heater hose. Won't hold up to vacuum long term if it is.

Why not punch your zipcode in here and see if there is any near you.

http://www.oreillyauto.com/site/c/detail/GAT0/2723...;ppt=C0267

Fri Dec 19, 2014 9:46 pm

I really don't know what the hose will hold up to but it's been fine in the other bus. I have a hard time finding the correct wire reinforced hose. I was even thinking about ordering some NOS stuff but it was pretty spendy.
I'll pick up some of that gates brand as well and compare the two but I notice it doesn't have the wire in it either.
Just took it out for a drive and it's running great. Thanks again.