PD41A float height?

[MarkCR750]

Quick question, I read that PD41A carb float heights should be 12.5 mm, does anyone know if that’s correct, thanks Mark.

[K2-K6]

I can only find the same as you've posted for the 41a.


The 42 is definitely 14.5 in manuals I have,  and in cross reference charts they show that correctly and the 41a at 12.5.

http://www.hondachopper.com/garage/carb_specs/carb_specs.html

A rough guide though for these flat base floats is that they generally sit parallel to the gasket face or they'd have to specify a point at which you should measure to spec.  So just holding them up when rested against needle should give some confirmation.

[MarkCR750]

Thanks K2 K6, I’ve set them at 12.5mm, I’ll check the levels with a clear tube tomorrow then carbs back on and see how she goes.

[MarkCR750]

Good news it’s running beautifully, no crackles and pops on the overrun, pulls smoothly through the range, the No1&4 plugs are tan centre dark grey outer, I’ll have a look at 2&3 when I can be bothered with the faf of taking them out but I expect them to be the same from the way it’s running, old pilots pulled out easily with just pliers, tapped new ones gently in with a flat face drift, old pilots were 35’s they were dirty and partially blocked, bright new 40’s fixed the lean bottom end, I very carefully set the floats to 12.5mm then attached a remote fuel tank with the carbs supported level on my BD workmate, I checked the actual levels using a clear plastic tube on the drains, 2,3,4 were fine with the level of fuel in the tube coinciding with the bowl gasket but No1 was about 5mm high so I readjusted the float height in No1 and got the actual level to match the other 3, I guess there may have been a slight bend in the float support arms but they all looked straight, anyway nice now, noticed the brakes weren’t as good as I remembered so bled them, left was fine but got air and dark fluid from the right, brakes are now very good again, all in all a good day in the garage! 🙂

[K2-K6]

Nice work,  it's good to get through a plan to improve something with success at the end of it.

I suppose most of these age carbs sitting for so many years are going to have some sort of impairment of idle circuits at least.

Out of interest, is it your set up that you are running std bellmouths inside the filter pods?

[MarkCR750]

It’s a bit of both K2 K6, I initially fitted a set of cheap cone pods, I found the bike hesitated during quick throttle demands and didn’t want to hold constant speeds, it sort of “surged”, I reasoned that Honda has fitted the rubber belmouths in the OE air box for a reason, so I grafted the pods onto the original rubber belmouths, problem solved, my guess is that the pods caused turbulence in the intake airflow which caused the carbs not to draw fuel correctly through the jets, as I said Honda wouldn’t have wasted money on the rubber belmouths if they weren’t needed, I do want to move to alloy belmouths only at some point but haven’t seen any that I like at the right price yet. [ Guests cannot view attachments ]

[hairygit]

The problem with unfiltered bellmouths is you may as well stick a teaspoonful of valve grinding paste through each plughole and get the same result. Before people give it "it works on race bikes" crap, race bike engines are rebuilt every couple of races! A rebuilt engine running without filters will start showing ring wear after just a couple of thousand miles, again, why do people think Honda fitted filters? After all, would you run your motor without the oil filter fitted?

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[Bryanj]

The Yam TZ 750 was
Rings 4 times a year minimum
Pistons every other set of rings
Crank and Barrels yearly
Crankcases every other year

[MarkCR750]

It’s true that engines draw a monumental amount of air when running and hence dust/grit and therefore an unfiltered intake will increase wear but on bikes such as this (low mileage weekend toys) it’s something that I can tolerate , I.e. rebuild in 5 years time instead of 25!.

[K2-K6]

[ Guests cannot view attachments ]

Hmmmmm bellmouths 

[MarkCR750]

Blimey, what’s that?

[K2-K6]

It's a BMW V8 an M5 I think.

Those two outlying and isolated intake either scavenge or are scavenged from on a 90degree crank V8,  so they arrange with separation to prevent a couple of cylinders running leaner than others.

It just shows how much is going on, invisible to our eyes generally, with intake dynamics. 

[hairygit]

But the bellmouths on that are drawing filtered air only once the cover on that chamber is fitted. My issue with open bellmouths on a bike is the lack of good filtration.

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[Erny]

Good news it’s running beautifully, no crackles and pops on the overrun, pulls smoothly through the range, the No1&4 plugs are tan centre dark grey outer, I’ll have a look at 2&3 when I can be bothered with the faf of taking them out but I expect them to be the same from the way it’s running, old pilots pulled out easily with just pliers, tapped new ones gently in with a flat face drift, old pilots were 35’s they were dirty and partially blocked, bright new 40’s fixed the lean bottom end, I very carefully set the floats to 12.5mm then attached a remote fuel tank with the carbs supported level on my BD workmate, I checked the actual levels using a clear plastic tube on the drains, 2,3,4 were fine with the level of fuel in the tube coinciding with the bowl gasket but No1 was about 5mm high so I readjusted the float height in No1 and got the actual level to match the other 3, I guess there may have been a slight bend in the float support arms but they all looked straight, anyway nice now, noticed the brakes weren’t as good as I remembered so bled them, left was fine but got air and dark fluid from the right, brakes are now very good again, all in all a good day in the garage!

Where did you source new pilots 40?

[MarkCR750]

NRP carbs, you can google them.