It runs!!!

[MonzaMan]

Hello all:


So after 20 years of neglect, turns out the bike needed some wiring replaced (new stator leads), tank and carb cleaned, new fluids, fresh battery, new points and condenser. After picking way at this through the summer, voilà!

Here is proof!

https://i.imgur.com/ZoG8ME7.mp4

https://i.imgur.com/jSeGRXE.mp4



As you can see, my son had to rescue me with my trailer so the success was short lived.

This is a 68 widecase Monza 250, and I am running a VHB30 square slide carb. I think the issue is clogging of the idle jet airway. But I am looking for advice on the set-up of this carb. Should I start a new thread for that?

Have a great day everyone!

David (aka MonzaMan)
Ottawa, Ontario

[Duccout]

Do you have fuel filters in the fuel lines? That might be a good move. Have you jetted the card as per the standard 29mm 250 carb? That would be a good place to start.


Cheers,


Colin

[Ventodue]

Congratulations, David. Look good - even your boy has a grin on his face .

Reckon Colin's advice is good, btw. A 45 idle jet should work ...

[mrkprsn]

I second the fuel filters. If you haven't used the bike in a while there will be little flakes of stuff that gets in the fuel. The pilot jet is really small. It doesn't take much to clog it.

[MonzaMan]

Thanks for the suggestions.

I cleaned the hell out of the tank with a long piece of heavy chain and gasoline during the resurrection. I know it's not perfect, but a start.

The plug is (and always was during the bike's previous life) wettish. It never liked the starting circuit activated. This time it did like the 'choke' until it something went amiss on that first ride. When I got home the plug was tan but very dry, even after starting attempts.

The plastic disc filter under the banjo on the VHB30 showed no signs of catching debris.

I cleaned up the jets anyway and it did make a minor improvement. It would start then die as soon as I touched the throttle. So I took the carb off and really cleaned up the jets. The main jet was partially clogged. Assembled everything and it seems worse. I can only get a quick fart and die and only after drying off the plug and trying. Plug wetness has returned in full force.

I did notice the idle jet is 70. Most big twins with these carbs use 60ish.

I am about to buy some new jets, but I am puzzled as to how it could have run well with this carb 20 years ago. Also, Henry Hogben sold me this carb - so I would be surprised if there was no logic to that large size. So my guess is that the air passage to the emulsion tube has somehow become clogged. Does this make any sense?

I really appreciated all possible input!


Best,

David

[Duccout]

Hi David,

As the bike was running fine, then I would not make any changes until you solve the problem, as you may create an issue where there was not one. The wet plug indicates flooding, so make sure that the float needle is sealing properly, also, a common problem is the cold-start plunger not sealing the jet properly, allowing flooding, so check this and also make sure that there is free-play in the cold-start cable. I would also have a look at the points and make sure that the gap has not closed up.

Good luck,

Colin

[blethermaskite]

David, As Colin has just referred to, check that choke slide, (I don't use those VHB carbs, and don't like them!) but if I remember correctly the choke slide has a little rubber sealing button on its bottom face which closes off the enrichening circuit, If the button is hard or damaged fuel can leak at this point and really mess up your carburation .........hope my memory isn't playing tricks on me......if I am wrong just ignore the above
Cheers,
George

[mrkprsn]

Sorry for the formatting. Do you have large (Mark 3) or small (Monza) valves?

BOLOGNA FACTORY STANDARD SINGLES

Model Year Dell'Orto type Size Needle Main Pilot Slide Needle pos. Needle jet

60 Sport 1950-51 MA16B 16 D15 70 45 50 2 260B
98N 1952-58 MA16B 16 D12 75 35 40 2 260B
98T 1952-58 MA16B 16 D12 75 35 40 2 260B
98TL 1953-58 MA16B 16 D12 75 35 40 2 260B
98S 1953-58 MA18B 18 D16 82 35 60 2 260B
98 Super Sport 1954-55 MB20B 20 E10 72 35 50 - -
55E 1955-57 14MFC Weber Carb. 60 45 - - -
55R 1955-57 14MFC Weber Carb. 60 45 - - -
55M 1955-57 14MFC Weber Carb. 60 45 - - -
125T 1956-60 MA18B 18 D12 80 40 50 2 260A
125TV 1956-58 MB20B 20 E10 82 35 50 2 260B
85N 1958-60 ME15BS 15 G4 70 35 50 2 258A
85 Sport 1958-60 ME15BS 6v G4 70 35 50 2 258A
98TS 1958-60 ME16BS 16 G1 74 35 50 3 258A
175S 1957 MB22.5B 22.5 E14 98 80 40 2 260B
175T 1957 MB22B 22 E12 92 45 80 2 260B
125S 1957 MB20B 20 E9 78 38 70 3 262A
100 Sport 1958-60 MA18B 18 D17 78 35 50 2 260A
125 Sport 1958-65 UB20BS 20 E10 85 35 50 2 260B
125 Sport(opt) 1958-61 SS1 22C 22 R4 92 50 80 3 260
125TS (note 1) 1958 UA20BS 20 E10 85 35 50 2 260B
125TS 1959-65 ME18BS 18 G4 76 38 50 3 258B
175 Americano 1958 MB22B 22 E12 92 45 80 2 260B
175 Sport 1958-61 UB22.5BS2 22.5 E14 98 40 80 2 260B
175 Sport(opt) 1959-61 SS1 25A 25 M14 120 50 100 2 265
175 Tourist 1958-61 MB22B 22 E12 92 45 80 2 260B
175TS 1958-60 MB22B 22 E12 92 45 80 2 260B
200 Elite 1959-65 UBF24BS 24 E10 98 40 70 2 260B
200 Super Sport 1959-62 UBF24BS 25 E10 98 40 70 2 260B
200 Super Sport(opt) 1959-62 SS1 27A 27 M13 108 50 80 3 265
200 Americano 1959 UBF24BS 24 E10 92 40 70 2 260B
200 Motocross 1959-60 SS1 27A 27 M13 105 50 80 3 265
200TS 1960-61 UBF24BS 24 E10 92 40 70 2 260B
200GT 1962 UBF24BS 24 E111 95 40 70 2 260A
250 Monza (narrow case) 1961-67 UBF24BS 24 E11 108 40 70 2 260B
Diana Europe 1961-64 UBF24BS 24 E11 103 35 70 2 260A
Diana USA 1961 UBF24BS 24 E11 108 40 70 2 260B
Diana Mk3 USA 1962-65 SS1 27D 27 M14 120 50 100 2 265
Diana Mk3 USA 1966-67 SS1 29D 29 M14 125 50 60 2 265
250 Mark 3(narrow case) 1967 SS1 29D 29 M14 125 50 60 2 265
250 Scrambler(narrow) 1962-67 SS1 27D 27 M14 112 50 100 3 265
Mach 1 1964-66 SS1 29D 29 M14 122 50 60 2 265
250GT 1964-66 UBF24BS 24 E19 108 40 60 2 260B
250 Monza(wide case) 1968 UBF24BS 24 E11 108 45 80 2 260H
250 Mark 3(wide case) 1968-69 SS1 29D 29 M14 112 45 60 2 260
250 Mark 3(wide case) 1970-74 VHB29AD 29 V13 110 40 40 2 265M
250 Mark 3D 1968-69 SS1 29D 29 M14 115 45 60 2 -
250 Mark 3D 1970-71 VHB20AD 20 V13 110 40 40 2 265M
250 Scrambler(wide) 1968-69 SS1 27D 27 M14 112 50 80 3 265
250 Scrambler(wide) 1970-73 VHB26BD 26 E17 95 45 40 2 260R
250 Desmo 1971-74 VHB29AD 29 V13 110 40 40 2 265M
239 Desmo 1974 PHF30AD 30 K3 125 65 503 2 265AB
239 Mark 3 1974 PHF30AD 30 K3 125 65 503 2 265AB
Monza Junior 1964-67 UB22BS 22 E16 98 42 60 2 260A
Piuma Standard 1961-68 T4 12D1 12 A4 58 - - 2 1-210
Piuma Sport 1962-66 UAO15S 15 C1 68 45 65 3 260
Piuma De-Luxe 1962-67 T4 12D1 12 A4 58 - - 2 1-210
Brisk 1961-67 T4 12D1 12 A4 58 - - 2 1-210
Sport 48 1962-65 UAO15S 15 C1 68 - 45 3 260
180 Standard 1962-63 ME15BS 15 G1 63 40 - 3 258A
Sport 80 1962-63 UA18S 18 C1 92 35 55 3 260
49SL 1964-65 UA15S 15 C1 68 45 65 3 260
100 Cadet (51mm bore) 1964-66 UA18S 18 C2 82 38 50 2 260
100 Cadet (52mm bore) 1967 UBF24BS 24 E2 102 40 70 2 260A
100 Mountaineer (51mm) 1964-66 UA18S 18 C2 82 38 50 2 260
100 Mountaineer (52mm) 1967 UBF24BS 24 E2 102 40 70 2 260A
Brio 48 1963-66 SHA14 12 12 - 52 40 6493/01 - -
Brio 50 1967-68 SHA14 12 12 - 56 40 6108/01 - -
Brio 100 1964-68 SHB18 16 16 - 82 40 6493/01 - -
Brio 100/25 1968 SHB18 16 16 - 88 50 6493/02 - -
48 Cacciatore 1964-67 UA15S 15 C1 68 45 65 3 260
50SL 1966 UA18BS 18 D10 85 40 55 1 260F
50SL/1 1967-68 UAO18S 18 D10 85 40 55 1 260F
50SL/2 1968-69 UAO18S 18 D10 85 40 55 1 260F
Rolly 50 1968 SHA14 12 12 - 52 40 6493/01 1 -
50 Scrambler 1969-70 UA18BS 18 C8 85 40 50 3 260F
100 Scrambler 1969-70 UBF24BS 24 E2 102 40 70 2 260A
125 Cadet/4 1967 ME18BS 18 G3 85 38 50 2 258A
125 Cadet/4 Motocross 1967 ME18BS 18 G3 85 38 50 2 258A
Sebring(narrow case) 1965-67 UBF24BS 24 E16 108 40 70 2 260A
Sebring(wide case) 1968 UBF24BS 24 E16 108 40 70 2 260A
350 Scrambler 1968-69 SS1 29D 29 M14 125 50 100 2 265
350 Scrambler 1970-74 VHB29AD 29 V13 110 40 40 2 265M
350 Mark 3 1968-69 SS1 29D 29 M14 112 45 60 2 260
350 Mark 3 1970-74 VHB29AD 29 V13 115 40 40 2 265M
350 Mark 3D 1968-69 SS1 29D 29 M14 115 45 60 2 260
350 Mark 3D 1970-71 VHB29AD 29 V13 120 40 40 2 265M
350 Desmo 1971-74 VHB29AD 29 V13 118 40 40 2 265M
450 Scrambler 1969-74 VHB29AD 29 V17 130 50 60 2 265T
450 Mark 3 1969-74 VHB29AD 29 V7 135 50 60 2 260T
450 Mark 3D 1969-71 VHB29AD 29 V8 135 50 60 2 260T
450 Desmo 1971-74 VHB29AD 29 V8 135 50 60 2 260T
450R/T (open pipe) 1971-72 VHB29AD 29 V7 140 50 60 2 265T
450T/S 1971-73 VHB29AD 29 V7 135 50 60 2 265T
450 Mark 3 Tourer 1970-72 VHB29AD 29 V7 130 50 60 2 265T
Regolarita 1975-76 PHB30BS 30 K3 125 65 50/3 2 265AB
Six Days 1977 PHBE32GS 32 K1 140 55 40 2 265AR
125 Scrambler 1971 375/20 amal 20 A1 95 12 373/3 1 105/DA


BOLOGNA FACTORY PRODUCTION ROAD RACERS

Model Year Dell'Orto type Size Needle Main Pilot Slide Needle pos. Needle jet

98 Competizione 1955 SS1 20C 20 R4 88 50 70 3 260
125 Gran Sport 1956 SS1 20C 20 R4 80 45 70 3 260
175 Gran Sport 1957 SS1 22.5C 22.5 R4 98 50 70 3 260
175 Formula 3 1959 SS1 27A 27 M14 108 50 80 3 260
220 Grand Prix 1960 SS1 29A 29 M14 115 50 80 3 260
250 Formula 3 (Manxman) 1961 SS1 29A 29 M14 118 50 100 3 260
250 Mach 1/s 1965 SS1 30A 30 M14 132 50 60 2 260

[MonzaMan]

I am quite sure I have the large valves. If I am not mistaken, they were tulip shaped. The seats were pretty bad. Instead of replacing them, the local machine shop made new ones for me to match. It wasn't expensive.

What a treasure of carb specs information that is - Thank you Mrkprsn! I gather Mark 3 is likely the closest match to my bike?

George - I looked at the bottom of the plunger and it does have a rubber seat. It did not look damaged but it did have a small kind of concentric depression. Basically you can see the outline of what it is seating against. I gather that rubber seat is not replaceable because I did install a carburettor kit from Dellorto and there was no such part in the kit... Any suggestions as to how one would check if it is seating correctly?

Does anyone use a VHB carb with these singles?

On some forums (Laverda, Guzzi), I have read about the air passage being fouled and constricting air and causing a rich idle mixture or flooding. I am going to have a look in from the top and try soaking that passage with carb cleaner...


Thank you!

[Ventodue]

I'll say it again. Your idle jet is too big.

Look at the data that Mark posted. To make things easier, I've cleaned and sorted them. There are three 250s that were fitted with VHBs. All of them used smaller idle jets that you have.

250 VHBs.jpg