Dolmar 5105 Intake Boot

[RedFir Down]

Afternoon fellas.

I have a Dolmar 5105 on the bench that has an air leak where the intake boot and cylinder meet.
I'm not seeing any intake boots available on line.
Do you know if they are available?
Or is safe to silicone the boot to the cylinder?

Thanks in advance!

 

[huskihl]

There’s a spring that wraps around and holds it on. Motoseal works. Don’t know about silicone

 

[RedFir Down]

That's what I meant, I have motoseal so I'll use that.
And yes the spring is in place.

The boot will hold about 5 psi but start leaking after that.
The saw holds a tune for about 5 seconds at WOT than it revs to the moon.

Thanks Kevin!

 

[drf256]

You sure it’s the boot? At WOT, I’d imagine there is nearly Zero vacuum in the boot.

 

[RedFir Down]

You sure it’s the boot? At WOT, I’d imagine there is nearly Zero vacuum in the boot.

That's where I was getting the air leak from.
In my little brain I would think just the opposite, at wide open throttle there would be a lot of vacuum where the boot meets the cylinder.
Can you explain your thoughts?
Thank you.

 

[drf256]

When the throttle butterfly opens, vacuum suddenly drops. Air takes path of least resistance, which should be through Venturi. Plus, you don’t get symptoms of runaway until 5 seconds in.

Sounds like you are running out of fuel, and as the saw winds up it gets worse.

You could be opening a massive air leak, like a tear in the boot. I usually see issues like you are having with fuel delivery issues or a bad tank vent. Carb metering side gets sucked dry. Could be bad impulse, bad fuel line/filter, carb, etc.

Could still be your boot, just doesn’t sound like it.

Vacuum won’t be zero, but would be low. Also sounds like you checked pressure and not vacuum.

 

[RedFir Down]

When the throttle butterfly opens, vacuum suddenly drops. Air takes path of least resistance, which should be through Venturi. Plus, you don’t get symptoms of runaway until 5 seconds in.

Sounds like you are running out of fuel, and as the saw winds up it gets worse.

You could be opening a massive air leak, like a tear in the boot. I usually see issues like you are having with fuel delivery issues or a bad tank vent. Carb metering side gets sucked dry. Could be bad impulse, bad fuel line/filter, carb, etc.

Could still be your boot, just doesn’t sound like it.

Vacuum won’t be zero, but would be low. Also sounds like you checked pressure and not vacuum.

Thanks for the explanation, it makes sense.
The tank vent is venting properly, I installed a new filter and swapped the carb with a known good one. All with the same results.
One thing I did notice was the fuel line was a tad bit on the soft side so it might be collapsing.
I checked both vacuum and pressure with the same results from both.

I'll get this "fabulous" piece of German engineering back together and see what I got (its so fun pulling the cylinder just to get to the intake boot).

Thanks again.

 

[drf256]

So you can only hold 5mm of vacuum?

Don’t get me wrong, a little Dirko on the boot won’t do anything bad, nor will appropriately tending to a vacuum leak.

See if it fixes the issue.

Where is the impulse line on the model?

 

[RedFir Down]

So you can only hold 5mm of vacuum?

Don’t get me wrong, a little Dirko on the boot won’t do anything bad, nor will appropriately tending to a vacuum leak.

See if it fixes the issue.

Where is the impulse line on the model?

Sorry for the delay.
Yes, it will hold 5 psi of vacuum anything higher and it will start to leak.
It's a hose that runs from the base of the cylinder to the intake adapter if you will. I cant log in with my phone to post a picture.
I got it sealed up last night so tomorrow I will have time to pressure / vac test it.

 

[cuinrearview]

Unscrew the intake spring ends from each other, clip about five winds off of the female end and screw it back together. Then check it again.

 

[RedFir Down]

Unscrew the intake spring ends from each other, clip about five winds off of the female end and screw it back together. Then check it again.

I didn't look at the spring that close when I had it off but that is a good idea. I have it back together now and we'll see how the motoseal does tomorrow. Thank you.

 

[RCBS]

https://www.sawagain.com/dolmar-ps-...rburetor-boot-suction-hose-new-oem-181131040/

They only have 1.