Board index

My Home Page

PilotOdyssey.com By hoser...


PilotOdyssey.com Chat Room

PilotOdyssey.com Photo Album

* Login   * Register * FAQ
http://www.pilotodyssey.com/PO/adm/images/imagemenu/smiley_cool.png PilotOdyssey.com Chat    http://www.pilotodyssey.com/PO/adm/images/imagemenu/find.png PilotOdyssey.com Google Search    http://www.pilotodyssey.com/PO/adm/images/imagemenu/emoticon_tongue.png FL400 Parts    http://www.pilotodyssey.com/PO/adm/images/imagemenu/emoticon_grin.png FL350 Parts    http://www.pilotodyssey.com/PO/adm/images/imagemenu/emoticon_evilgrin.png FL250 Parts    http://www.pilotodyssey.com/PO/adm/images/imagemenu/emoticon_unhappy.png Admin Email   
It is currently Thu Mar 28, 2024 11:58 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 17 posts ] 
Author Message
 Post subject: 670 pilot project
PostPosted: Mon Jul 16, 2018 3:53 pm 
Offline

Joined: Thu Apr 29, 2010 12:53 am
Posts: 1430
Location: Norco, CA
As some may know I have decided rather than do a rebuild on the pilot Engine to do a transplant with a 670 rotax.
Pictures to follow, in short I got a great deal on most of a kit and selling off pilot parts no longer needed has made the project very affordable.
I am at the point where I started it up over the weekend and actually drove it into the garage :-)

now for the questionable parts, I have not yet checked the compression on the Engine, I do know it has new pistons installed, for me it seems to cranks over way too fast makes me question the compression, that is definitely on the list to check. it has dual SBN30 watercraft carbs, this is another questionable issue, I am not sure if they are plumbed correctly or not but I am thinking I should be seeing some return fuel flow back to the tank and I am not. the pump internals look good but maybe when I was inspecting I overlooked something.
It does run, seems to start easy so at this time the 2 things which have me concerned is the compression, wondering if the builder just put in new pistons or did they do a bore job? And the other is the carburation and built in fuel pump. it is also very sluggish to respond off idle which if I read the SNB manual correctly could be due to too high of pop-off pressure which I suspect if I am not flowing anything back to the tank I either don't have enough fuel flow from the pump to make pressure or something else is going on?

Looking for some insight, also recommended jetting for the SBN38 carbs.


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Mon Jul 16, 2018 10:56 pm 
Offline

Joined: Tue Aug 03, 2010 12:02 am
Posts: 2147
Location: St. John, Washington
The rotax ia going to sound a lot quicker with the electric starter than a sigle cylinder pilot you are used to.

Not sure on the SBN30 carburetors, but the BN38i dual carbs i am running a 160 up to 165 main with a 70 pilot. Black popoff spring and a 2.3 needle. this is on a 98 670HO. the HO had a flat top piston and a bit more of a closed combustion chamber. Not sure what that means for fuel needs between the 670 and the HO


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Tue Jul 17, 2018 12:44 am 
Offline

Joined: Thu Apr 29, 2010 12:53 am
Posts: 1430
Location: Norco, CA
I had a typo they are the mikuni 38 watercraft carbs.
compression is quite low but in the rotax manual I can only find information about corrected combustion somewhere around 6.2 and 6.8, from what I read that is from the point the exhaust port is covered. I'm only measuring about 100-105 psi but 14.7 (atmosphere) x 6.8 = 100, so I'm cornfused, seems low but calculates correct what am I missing? it fires right up but doesn't show any flow out of the PTO carb? with the low compression am I getting a low pulse and not operating the pump fully.


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Tue Jul 17, 2018 1:26 am 
Offline

Joined: Thu Apr 29, 2010 12:53 am
Posts: 1430
Location: Norco, CA
Attachment:
File comment: Radiator mount, made a cradle that bolts on to seat belt mounts and the top bolts to the cage
20180713_200509.jpg
20180713_200509.jpg [ 50.93 KiB | Viewed 3066 times ]

Attachment:
File comment: Fuel tank mount, used the radiator cross bar mount
20180624_101841.jpg
20180624_101841.jpg [ 95.47 KiB | Viewed 3066 times ]

Attachment:
File comment: Velocity stacks, 2.75 90 degree boots will go on the adapt filters
20180624_101340.jpg
20180624_101340.jpg [ 111.42 KiB | Viewed 3066 times ]


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Tue Jul 17, 2018 1:28 am 
Offline

Joined: Thu Apr 29, 2010 12:53 am
Posts: 1430
Location: Norco, CA
Sorry about the sideways picture, I hate when that happens.
Apparently the smart phone Isn't all that smart


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Tue Jul 17, 2018 2:09 am 
Offline

Joined: Thu Apr 29, 2010 12:53 am
Posts: 1430
Location: Norco, CA
Haha, just noticed, I got the comments mixed on the carbs and radiator


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Tue Jul 17, 2018 10:43 pm 
Offline

Joined: Thu Apr 29, 2010 12:53 am
Posts: 1430
Location: Norco, CA
nitrosport_5 wrote:
The rotax ia going to sound a lot quicker with the electric starter than a sigle cylinder pilot you are used to.

Not sure on the SBN30 carburetors, but the BN38i dual carbs i am running a 160 up to 165 main with a 70 pilot. Black popoff spring and a 2.3 needle. this is on a 98 670HO. the HO had a flat top piston and a bit more of a closed combustion chamber. Not sure what that means for fuel needs between the 670 and the HO


Nitro, I was just reading one of your posts on the dootalk forum what did you finally do about the CDI (Capacitor Discharge Ignition) and the DPM setup, not really sure what that is but sounds like it messes with the timing.


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Thu Jul 19, 2018 10:00 am 
Offline

Joined: Fri Jul 04, 2014 7:33 am
Posts: 1070
Dual sbn38 carbs normally only run one single fuel pump on the rear carb which feeds both carbs. There is a pin-hole restrictive passage on the front carb this which helps to raise the fuel pressure. Speaking of which, pressure should be between 1.5~6psi at WOT (Wide Open Throttle). Also watercraft carbs are a closed loop fuel system which means - remove all tank vents. Use a one-way inlet instead as with watercraft. The system needs to fully operate under pressure. This leads to me explain popoff pressure which is adversely related to fuel pressure. On duel 38s, you want the popoff pressure to ideally be above 20psi. Bottom corrections can be made with the low screw at 1.25 turns, and 75~80 pilot jet. Aim a good idle at 1.25 turns on the low screws and adjust pop and pilot jet to make it happen at 1.25 turns. High screws can go out to 1 turn for safe operations or 2.5 turns for tuning objectives; but the High screws should end at 1 turn with a properly jetting main. At 2.5 turns, WOT (Wide Open Throttle) would be protected, but 3/4 throttle would run lean - meaning up the main!

On watercraft, these carbs usually run a 130-135 main jet for stock 700cc engines (Yamaha) but often they are updated with about a 140-142.5 main jet depending on modifications.


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Thu Jul 19, 2018 10:08 am 
Offline

Joined: Fri Jul 04, 2014 7:33 am
Posts: 1070
Re-read. Fuel should be returning to the tank for sure otherwise I suspect a blockage (too much fuel pressure!) or the pump body isn’t working right. It could also be a leaky Engine. 100psi sounds low. Test at WOT (Wide Open Throttle)?

Check on the pump, the circular diaphragms. Often they will crease and stop pumping especially if the Engine backfired at one point.

Check reeds.

Sbn38 pumps are very strong! Fuel should practically be squirting back to the tank.


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Thu Jul 19, 2018 3:30 pm 
Offline

Joined: Thu Apr 29, 2010 12:53 am
Posts: 1430
Location: Norco, CA
So, I'm a little confused, if the pump only does 1.5 to 6 psi, what supplies the 22 psi for the pop-off pressure?
yes definitely agree, 100 psi is low, when you say leaky Engine, are you talking rings, seals, rotary valve? I'm suspecting that there could be some leakage from the rotary valve drive to the Engine as it appears that the oil level is going down from my reservoir, using a brake fluid rezi for this. also seems to be smoking more than expected but it really has not had a chance to get hot and burn off any excess oil in the crank case, if return fuel system is plugged it must be pumping to much fuel into the Engine.
I pulled the head off yesterday as I thought is may have HO pistons with a non HO head, that was not the case, today I'll pull the cylinders and pistons and see if there is some obvious reason for the low compression.
I priced having the crank rebuilt, seems like just shy of $500, if possible I'll hold off on that expense.

Yes, compression was taken WOT (Wide Open Throttle).


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Thu Jul 19, 2018 11:21 pm 
Offline

Joined: Fri Jul 04, 2014 7:33 am
Posts: 1070
Popoff is acyrately set with a Mikuni popoff pressure gauge. It’s a glorified accurate bicycle pump. If you don’t have one then just follow the Mikuni popoff chart but beware - dual carbs will almost always have variance between the two unless checked with the popoff gauge.

Also with a power valve motor (( Internal Combustion Engine ? )), you want to check the compression with the valve lifted. You’ll actually get a lower psi reading, but lifted should be your trapped compression; while a lowered power valve will be in the dynamic ranges. Trapped is more important to know at baseline and is what you’ll basically be running most of the time at high rpm anyways. I’m not sure what compression that Engine should be, but as I understand it mixture won’t fire below 90psi on most 2-strokes.


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Fri Jul 20, 2018 9:53 am 
Offline

Joined: Thu Apr 29, 2010 12:53 am
Posts: 1430
Location: Norco, CA
Top end is off now, I'll be taking it you the shop that has been boring my cylinders for the last 30 years and get some measurements and see if we can figure why such low compression, they are new piston and the cylinders look good.
one thing I notice about this Engine, my first Rotax is how mismatched the crank case is to the cylinders, there is at least an 1/8" of material that would need to come out to match them up.
I also have a second 670 which had a piston go south, I may end up pulling that apart and possibly use that bottom end with this new top end.


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Fri Jul 20, 2018 5:20 pm 
Offline

Joined: Tue Aug 03, 2010 12:02 am
Posts: 2147
Location: St. John, Washington
Kuma wrote:
nitrosport_5 wrote:
The rotax ia going to sound a lot quicker with the electric starter than a sigle cylinder pilot you are used to.

Not sure on the SBN30 carburetors, but the BN38i dual carbs i am running a 160 up to 165 main with a 70 pilot. Black popoff spring and a 2.3 needle. this is on a 98 670HO. the HO had a flat top piston and a bit more of a closed combustion chamber. Not sure what that means for fuel needs between the 670 and the HO


Nitro, I was just reading one of your posts on the dootalk forum what did you finally do about the CDI (Capacitor Discharge Ignition) (Capacitor Discharge Ignition) and the DPM setup, not really sure what that is but sounds like it messes with the timing.


Left it all unhooked, seems to work just fine. If you have a 98-99 sled you must keep the tether switch because it acts as they key and is programmed to the CDI (Capacitor Discharge Ignition).


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Sat Jul 21, 2018 3:02 am 
Offline

Joined: Thu Apr 29, 2010 12:53 am
Posts: 1430
Location: Norco, CA
Top end seems ok, clearance good, ring gap good, possibly the cylinders were glazed during initial run in, I'm planning on pulling my other bottom end apart, clean it, possibly match port the case to the cylinders and try that. while I'm at it I'll go through the carbs again.


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Sat Jul 21, 2018 5:58 pm 
Offline

Joined: Thu Apr 29, 2010 12:53 am
Posts: 1430
Location: Norco, CA
Ya, the other bottom end I'm pretty sure is an OH, factory tunnel porting, the case matches pretty well with the cylinders so just a little matching and smoothing needed, I probably will not mess too much with the cylinder porting other than trimming and blending the cylinder base using an HO cylinder for guidance.


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Sat Jul 21, 2018 11:45 pm 
Offline

Joined: Fri Jul 04, 2014 7:33 am
Posts: 1070
Have a pro perform a quick hone to see if the bore is out of round? Did someone lift the exhaust port?


Top
 Profile E-mail  
 
 Post subject: Re: 670 pilot project
PostPosted: Sun Jul 22, 2018 4:04 am 
Offline

Joined: Thu Apr 29, 2010 12:53 am
Posts: 1430
Location: Norco, CA
I have a bore gauge, I can check it to see how straight it is.
the ports do not appear to have been touched,


Top
 Profile E-mail  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 17 posts ] 

All times are UTC - 5 hours [ DST ]


Who is online

Registered users: Bing [Bot], Duneit, eseymour72, Garemie, Google [Bot], Lanix, Q, wyeeoddy


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group