500W carb questions

Maestro, SEI-V
Canuck750
Posts: 111
Joined: 29 Jan 2018 22:14
Location: Edmonton, Alberta, C

500W carb questions

Post by Canuck750 »

My 1978 500W is running stock Dellorto carbs, an Elektronic Sasche ignition with dyna mini coils, engine has been rebuilt with new liners and pistons, rebuilt heads, rebuilt bottom end etc... I have retorqued the heads, the valve gap has been set with the engine cold, engine starts immediatly with the electric starter. Once warmed up the carbs have been synced, a strobe light with a warm engine shows the advance mark on the front cylinder appearing as it should at around 3500 rpm.

First problem: I have got the bike running pretty good, it idles nicely but the throttle will climb from time to time on idle, snap the trottle open for a second and the idle will drop back down. I checked for air leaks but can't seem to find any. Could the carb slide return springs be too weak?

I had the stock cable operated chokes set up but the front cable is too long and here is the second problem: cold engine, handlebar choke lever pulled to full choke, bike starts right up but fuel is dripping out of the left exhaust pipe header to muffler joint, if I turn off the choke lever the fuel drip stops and I can keep the bike running with some throttle until it warms up, then it idles ok. I removed the cable operated chokes to day installed a flip lever choke to the left carb, blanked off the right carb choke, have not tried running it yet.

Third problem, warmed up bike, at cruise speed in 3rd gear, say 40 mph, if I give it a fist of throttle it just bogs right down, I have the needle on the second notch, stock jetting. If I gently increase the trottle it runs ok.

Carbs have been ultrasonic cleaned, new jets and O rings.

Thanks in advance for any help

Jim
3potjohn
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Joined: 02 Jun 2007 13:58
Location: Devon

Re: 500W carb questions

Post by 3potjohn »

Could be a sticking float/leaky needle valve/ incorrect float height/pivot pin not seated/float rubbing on bowl.
If you switch off the fuel and ride does it improve before it runs out. Have you checked fuel volume in the floatbowls.
With the floatbowl removed observe fuel cut out when manually operating the float.
Can you smell petrol in the engine oil by the way?
John
Canuck750
Posts: 111
Joined: 29 Jan 2018 22:14
Location: Edmonton, Alberta, C

Re: 500W carb questions

Post by Canuck750 »

Thank you for the advice,

I replaced the viton tip fuel valves (hard and not pointed) and checked the float height (10mm to center of float measured from carb flange) one carb was a little less than 10mm about 8mm, no more fuel dribbling out of the left hand header to muffler joint on choke.

Runs a bit better when I give it throttle but it still seems like there should be more take off there. After about ten minutes on the highway at 65mph I took an off ramp and the bike struggled to hold 60 mph up the incline, after leveling off it seemed to recover some power. I did a plug check when I got back from an hours ride, both plugs are burning pretty clean and compression was 122 on the front and 126 on the rear, new pistons and rings are still breaking in to the new cylinder liners.

I had the stator rewound and it putting out good AC voltage at idle, about 35 AC volts climbing to aboiut 60 at half throttle. The DC output to the battery does not go over 12.2 volts, that seems low to me???

The bike came with a pair of Mihuni round slide cfarbs fitted, I may put them bacl on for comparison and see if there is betetr performance. I am a purist when it comes to OEM on bikes but I wowuld like it to have more power and response.
3potjohn
Posts: 1243
Joined: 02 Jun 2007 13:58
Location: Devon

Re: 500W carb questions

Post by 3potjohn »

I have one bike with cable operated chokes and replaced temporarily with flip up chokes when chasing a problem. In this instance it only proved this was not the issue. Are the chokes sealing correctly?
John
Seagreen
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Location: Cheltenham UK
Location: Cheltenham, Glos

Re: 500W carb questions

Post by Seagreen »

Could the problem be the ignition system rather than carburation? Weak/incorrect sparking could cause similar symptoms - timing may be good but if the coils are not generating sufficient HT then ?????? Just a thought.
Adios,
Charles
Canuck750
Posts: 111
Joined: 29 Jan 2018 22:14
Location: Edmonton, Alberta, C

Re: 500W carb questions

Post by Canuck750 »

I feel the same about a possible ignition problem other than carbs, I have heard many times that 90% of all carburation issues is ignition.
That said the Elektronic Sasche system was installed last fall with their new Dyna mini coils and new HT leads so I am hoping this is not the case. I am questioning the new electronic reg/rec however as the rewound stator (Westcounty windings) seems to be putting out plenty of AC current at idle and rising nicely with throttle. I would have thought the DC power out of the reg/red would be putting put close to 14volts rather than the 12.2 it is sending.

I spoke to the previous owner last night, he had the Mikuni 26mm carbs on the Morini (stamped 26 8074 on the carb body) and claimed the Mikuni carbs transformed the bike from in his words "a bag of hammers to a responsive, easy starting bike". He also told me that he could never get the Dellorto carbs to 'work' in his words.

I ultrasonic cleaned the Mikunis last night so today I will fit them and see what happens, fingers crossed.

Image

Image
Last edited by Canuck750 on 08 May 2022 02:37, edited 1 time in total.
Canuck750
Posts: 111
Joined: 29 Jan 2018 22:14
Location: Edmonton, Alberta, C

Re: 500W carb questions

Post by Canuck750 »

I installed the Mikuni carbs today, they slot right into the stock rubber boots, I think the air box boot even fits better than the Dellorto carbs. The mikunio have a lver choke, the one question I need to figure out is the mixture screw, its on the inside of the crab so not easyly accessable to adjust, I don't know if on Mikuni this mixture screw is controlling air or fuel?? I have them set at 1 1/2 turns out, turning the screws in or out does not seem to make any difference. Until I sort out the reg/rec charging issue ots probably a mute point.

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The good news is the bike idles much smoother, it responds much better as well, a win!

The bad news is that the new solid state electronic reg/rec is not puitting out a DC charge to the battery and after about a half hour on the road the battery power is falling enough to effect the ignition. I need to speak to the manufacturer tomorrow to find out whta is up.
Last edited by Canuck750 on 08 May 2022 02:38, edited 1 time in total.
Canuck750
Posts: 111
Joined: 29 Jan 2018 22:14
Location: Edmonton, Alberta, C

Re: 500W carb questions

Post by Canuck750 »

Turns out the reg problem was just a bad crimp connection on the red DC lead to battery, crimped pn a new eyelet and the reg/rec is keeping the battery at 13.5 volts, hurrah!
Canuck750
Posts: 111
Joined: 29 Jan 2018 22:14
Location: Edmonton, Alberta, C

Re: 500W carb questions

Post by Canuck750 »

Ok I finaly got to experience that perfect moment,

the 500W is a wonderful bike to ride, I have read and heard how good the Morini's are but until this week my bike was never properly sorted, now that the ignition, charging, carburatuion and foot controls are sorted its just great!

I have owned and still own a lot of different 1970's Italian motorcycles including Guzzi V7 Sport, 750S, 850 Lemans, Ducati bevel twins amongst others and this 500 is the nicest bike to ride, its smooth, it handles great and its nice and light.

Now to get my 1975 3-1/2 Strada motor rebuilt.
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Daddy Dom
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Re: 500W carb questions

Post by Daddy Dom »

Excellent result! (We knew that :wink: )

Yours is the only one I've seen with Mikunis. You'll miss out on all the Dell 'Orto jet-size conversations.
DD
MRC 3082½
MickeyMoto
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Re: 500W carb questions

Post by MickeyMoto »

Daddy Dom wrote: 28 May 2021 03:04 Excellent result! (We knew that :wink: )

Yours is the only one I've seen with Mikunis. You'll miss out on all the Dell 'Orto jet-size conversations.
DD
There are still the oil and tyre conversations to be had occassionally!
3potjohn
Posts: 1243
Joined: 02 Jun 2007 13:58
Location: Devon

Re: 500W carb questions

Post by 3potjohn »

That is really good news.Adding up my motorcycle history, I have had 28 carbs but am convinced I still have carb trouble on one bike, in mid throttle. If I had some Mikunis I would give them a try.
John
huub
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Joined: 24 Jul 2006 15:11

Re: 500W carb questions

Post by huub »

Mikuni's are stupidly cheap, i have a set of 34 mm Chinese made mikuni's on my guzzi.
A set of new mikuni's was cheaper than changing the dellorto floats.
Canuck750
Posts: 111
Joined: 29 Jan 2018 22:14
Location: Edmonton, Alberta, C

Re: 500W carb questions

Post by Canuck750 »

Daddy Dom wrote: 28 May 2021 03:04 Excellent result! (We knew that :wink: )

Yours is the only one I've seen with Mikunis. You'll miss out on all the Dell 'Orto jet-size conversations.
DD
Ah yes the joy of jetting Delortos!

I just replaced the worn out Dellorto PHF 32 carbs in ny 75 Ducati 860 with a set of new PHF 36, the reccommended modern day replacement

Image

Supposedly plug and play HA! nonsense, there are many differences to the design and the tuning, I had to modify the intakes and the air box steel tubes to allow these new crabs to fit the stock attacments (wanting to keep the stovk look), the idle screws are completely different in design and in located in a different part of the carb body, the rear carb idle screw is now directly in line with a frame tube, the carbs need richer idle jets to run at all and the lean burn carbs are much more finicky to set up, been swappIng idle jets for a week now, and the new Dellortos were silly expensive compared to a set of Mikuinis.

I should have tried a pair of Mikuni carbs on the Ducati, still fighting a slight lean on the over run, slight crackling / popping.

Having the same lean tuning issue with a new pair of PHF 36 on my 73 Laverda SF1

I asked the previous owner how he figured out the Mikuni jetting?? He told me he emailed Sudco Mikuni and they asked for the type of motor (V twin 4 stroke, push rod heron head), the horespower and weight of the bike and SUDCO reccommended a carb size and shipped them jetted to their design, they just went on the bike and ran great with no alterations. Previous owner lived on the coast at sea level, I am in the praries at 645m above sea level and may lean out the pilot jets one size.

https://www.sudco.com/carburetors.html
Last edited by Canuck750 on 08 May 2022 02:40, edited 1 time in total.
huub
Posts: 194
Joined: 24 Jul 2006 15:11

Re: 500W carb questions

Post by huub »

I asked the previous owner how he figured out the Mikuni jetting?? He told me he emailed Sudco Mikuni and they asked for the type of motor (V twin 4 stroke, push rod heron head), the horespower and weight of the bike and SUDCO reccommended a carb size and shipped them jetted to their design, they just went on the bike and ran great with no alterations. Previous owner lived on the coast at sea level, I am in the praries at 645m above sea level and may lean out the pilot jets one size.
doing carb jetting over the phone, that is seriously impressing :shock:
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